ALBERT

Beschreibung: Polarization data from SCIAMACHY limb backscatter observations compared to vector radiative transfer model simulations Atmospheric Measurement Techniques Discussions, 5, 2221-2271, 2012 Author(s): P. Liebing, K. Bramstedt, S. Noël, V. Rozanov, H. Bovensmann, and J. P. Burrows SCIAMACHY is a passive imaging spectrometer onboard ENVISAT, designed to obtain trace gas abundances from measured radiances and irradiances in the UV to SWIR range in nadir, limb and occultation viewing modes. Its grating spectrometer introduces a substantial sensitivity to the polarization of the incoming light with nonnegligible effects on the radiometric calibration. To be able to correct for the polarization sensitivity, SCIAMACHY utilizes broadband Polarization Measurement Devices (PMDs). While for the nadir viewing mode the measured atmospheric polarization has been validated against POLDER data (Tilstra and Stammes, 2007, 2010), a similar validation study regarding the limb viewing mode has not yet been performed. This paper aims at an assessment of the quality of the SCIAMACHY limb polarization data. Since limb polarization measurements by other air- or spaceborne instruments in the spectral range of SCIAMACHY are not available, a comparison with radiative transfer simulations by SCIATRAN V3.1(Rozanov et al., 2012) using a wide range of atmospheric parameters is performed. SCIATRAN is a vector radiative transfer model (VRTM) capable of performing calculations of the multiply scattered radiance in a~spherically symmetric atmosphere. The study shows that the limb polarization data exhibit a large systematic bias which is decreasing with wavelength. The most likely reason for this bias is an instrumental phase shift which changes the relative contributions of different Stokes vector components to the PMD signal as compared to on-ground calibration measurements. It is also shown that it is in principle feasible to recalibrate the polarization sensitivity using the in-flight data and the VRTM simulations, enabling also the monitoring of its degradation. Together with an optimization of the algorithm used to calculate the in-flight polarization data an improved polarization correction can increase the radiometric accuracy of SCIAMACHY limb radiance spectra substantially.

Beschreibung: First intercalibration of column-averaged methane from the Total Carbon Column Observing Network and the Network for the Detection of Atmospheric Composition Change Atmospheric Measurement Techniques Discussions, 5, 1355-1379, 2012 Author(s): F. Forster, R. Sussmann, M. Rettinger, N. M. Deutscher, D. W. T. Griffith, N. Jones, and P. K. Patra We present the intercalibration of dry-air column-averaged mole fractions of methane (XCH 4 ) retrieved from solar FTIR measurements of the Network for the Detection of Atmospheric Composition Change (NDACC) in the mid-infrared (MIR) versus near-infrared (NIR) soundings from the Total Carbon Column Observing Network (TCCON). The study uses multi-annual quasi-coincident MIR and NIR measurements from the stations Garmisch, Germany (47.48° N, 11.06° E, 743 m a.s.l.) and Wollongong, Australia (34.41° S, 150.88° E, 30 m a.s.l.). Direct comparison of the retrieved MIR and NIR time series shows a phase shift in XCH 4 seasonality, i.e. a significant time-dependent bias leading to a standard deviation (stdv) of the difference time series (NIR-MIR) of 8.4 ppb. After eliminating differences in a prioris by using ACTM-simulated profiles as a common prior, the seasonalities of the (corrected) MIR and NIR time series agree within the noise (stdv = 5.2 ppb for the difference time series). The difference time series (NIR-MIR) do not show a significant trend. Therefore it is possible to use a simple scaling factor for the intercalibration without a time-dependent linear or seasonal component. Using the Garmisch and Wollongong data together, we obtain an overall calibration factor MIR/NIR = 0.9926(18). The individual calibration factors per station are 0.9940(14) for Garmisch and 0.9893(40) for Wollongong. They agree within their error bars with the overall calibration factor which can therefore be used for both stations. Our results suggest that after applying the proposed intercalibration concept to all stations performing both NIR and MIR measurements, it should be possible to obtain one refined overall intercalibration factor for the two networks. This would allow to set up a harmonized NDACC and TCCON XCH 4 data set which can be exploited for joint trend studies, satellite validation, or the inverse modeling of sources and sinks.

Beschreibung: Characterization and airborne deployment of a new counterflow virtual impactor inlet Atmospheric Measurement Techniques Discussions, 5, 1515-1541, 2012 Author(s): T. Shingler, S. Dey, A. Sorooshian, F. J. Brechtel, Z. Wang, A. Metcalf, M. Coggon, J. Mülmenstädt, L. M. Russell, H. H. Jonsson, and J. H. Seinfeld A new counterflow virtual impactor (CVI) inlet is introduced with details of its design, laboratory characterization tests, and deployment on an aircraft during the 2011 Eastern Pacific Emitted Aerosol Cloud Experiment (E-PEACE). The CVI inlet addresses three key issues in previous designs; in particular, the inlet operates with: (i) negligible organic contamination; (ii) a significant sample flow rate to downstream instruments (~15 l min −1 ) that reduces the need for dilution; and (iii) a high level of accessibility to the probe interior for cleaning. Wind tunnel experiments characterized the cut size of sampled droplets and the particle size-dependent transmission efficiency in various parts of the probe. For a range of counter-flow rates and air velocities, the measured cut size was between 8.7–13.1 μm. The percentage error between cut size measurements and predictions from aerodynamic drag theory are less than 13%. The CVI was deployed on the Center for Interdisciplinary Remotely-Piloted Aircraft Studies (CIRPAS) Twin Otter for thirty flights during E-PEACE to study aerosol-cloud-radiation interactions off the central coast of California between July and August 2011. Results are reported to assess the performance of the inlet including comparisons of particle number concentration downstream of the CVI and cloud drop number concentration measured by two independent aircraft probes. Measurements downstream the CVI are also examined from one representative case flight coordinated with shipboard-emitted smoke that was intercepted in cloud by the Twin Otter.

Beschreibung: Improved cloud screening in MAIAC aerosol retrievals using spectral and spatial analysis Atmospheric Measurement Techniques Discussions, 5, 1575-1595, 2012 Author(s): A. Lyapustin, Y. Wang, I. Laszlo, and S. Korkin An improved cloud/snow screening technique in the Multi-Angle Implementation of Atmospheric Correction (MAIAC) algorithm is described. It is implemented as part of MAIAC aerosol retrievals based on analysis of spectral residuals and spatial variability. Comparisons with AERONET aerosol measurements and a large-scale MODIS data analysis show strong suppression of aerosol optical depth outliers due to unresolved clouds and snow. At the same time, the developed filter does not reduce the aerosol retrieval capability at high 1 km resolution in strongly inhomogeneous environments, such as near centers of the active fires. Despite significant improvement, the optical depth outliers in high spatial resolution data are and will remain the problem to be addressed by the application-dependent specialized filtering techniques.

Beschreibung: Measuring variations of δ 18 O and δ 2 H in atmospheric water vapour using laser spectroscopy: an instrument characterisation study Atmospheric Measurement Techniques Discussions, 5, 1597-1655, 2012 Author(s): F. Aemisegger, P. Sturm, P. Graf, H. Sodemann, S. Pfahl, A. Knohl, and H. Wernli Variations of stable water isotopes in water vapour have become measurable at a measurement frequency of about 1 Hz in recent years using novel laser spectroscopic techniques. This enables us to perform continuous measurements for process-based investigations of the atmospheric water cycle at the time scales relevant for synoptic meteorology. An important prerequisite for the interpretation of data from automated field measurements lasting for several weeks or months is a detailed knowledge about instrument properties and the sources of measurement uncertainty. We present here a comprehensive characterisation and comparison study of two commercial laser spectroscopic systems based on cavity ring-down spectroscopy (Picarro) and off-axis integrated cavity output spectroscopy (Los Gatos Research). The uncertainty components of the measurements were first assessed in laboratory experiments, focussing on the effects of (i) water vapour mixing ratio, (ii) measurement stability, (iii) uncertainties due to calibration and (iv) response times of the isotope measurements due to adsorption-desorption processes on the tubing and measurement cavity walls. Based on the experience from our laboratory experiments we set up a one-week field campaign for comparing measurements of the ambient isotope signals of the two laser spectroscopic systems. The optimal calibration strategy determined for both instruments was applied as well as the correction functions for water vapour mixing ratio effects. The root mean square difference between the isotope signals from the two instruments during the field deployment was 2.3‰ for δ 2 H, 0.5‰ for δ 18 O and 3.1‰ for deuterium excess. These uncertainty estimates from field measurements compare well to those found in the laboratory experiments. The present quality of measurements from laser spectroscopic instruments combined with a calibration system opens new possibilities for investigating the atmospheric water cycle and the land-atmosphere moisture fluxes.

Beschreibung: Consistency between Fourier transform and small-volume few-wave decomposition for spectral and spatial variability of gravity waves above a typhoon Atmospheric Measurement Techniques Discussions, 5, 1763-1793, 2012 Author(s): C. I. Lehmann, Y.-H. Kim, P. Preusse, H.-Y. Chun, M. Ern, and S.-Y. Kim Convective gravity wave (GW) sources are spatially localized and emit at the same time waves with a wide spectrum of phase speeds. Any wave analysis therefore compromises between spectral and spatial resolution. Future satellite borne limb imagers will for a first time provide real 3d volumes of observations. These volumes will be however limited which will impose further constraints on the analysis technique. In this study a three dimensional few-wave appoach fitting sinusoidal waves to limited 3-D volumes is introduced. The method is applied to simulated GWs above typhoon Ewiniar and GW momentum flux is estimated from temperature fluctuations. Phase speed spectra as well as average profiles of positive, negative and net momentum fluxes are compared to momentum flux estimated by Fourier transform as well as spatial averaging of wind fluctuations. The results agree within 10–20%. The few-wave method can also reveal the spatial orientation of the GWs with respect to the source. The relevance of the results for different types of measurements as well as its applicability to model data is discussed.

Beschreibung: Effect of sampling variation on error of rainfall variables measured by optical disdrometer Atmospheric Measurement Techniques Discussions, 5, 8895-8924, 2012 Author(s): X. C. Liu, T. C. Gao, and L. Liu During the sampling process of precipitation particles by optical disdrometers, the randomness of particles and sampling variability has great impact on the accuracy of precipitation variables. Based on a marked point model of raindrop size distribution, the effect of sampling variation on drop size distribution and velocity distribution measurement using optical disdrometers are analyzed by Monte Carlo simulation. The results show that the samples number, rain rate, drop size distribution, and sampling size have different influences on the accuracy of rainfall variables. The relative errors of rainfall variables caused by sampling variation in a descending order as: water concentration, mean diameter, mass weighed mean diameter, mean volume diameter, radar reflectivity factor, and number density, which are independent with samples number basically; the relative error of rain variables are positively correlated with the margin probability, which is also positively correlated with the rain rate and the mean diameter of raindrops; the sampling size is one of the main factors that influence the margin probability, with the decreasing of sampling area, especially the decreasing of short side of sample size, the probability of margin raindrops is getting greater, hence the error of rain variables are getting greater, and the variables of median size raindrops have the maximum error. To ensure the relative error of rainfall variables measured by optical disdrometer less than 1%, the width of light beam should be at least 40 mm.

Beschreibung: On the effect of moisture on the detection of tropospheric turbulence from in situ measurements Atmospheric Measurement Techniques Discussions, 5, 8223-8240, 2012 Author(s): R. Wilson, H. Luce, H. Hashiguchi, M. Shiotani, and F. Dalaudier The present note addresses the detection of turbulence based on the Thorpe (1977) method applied to an atmosphere where saturation of water vapor occurs. The detection method proposed by Thorpe relies on the reordering in ascending order of a measured profile of a variable conserved through adiabatic processes (e.g. potential temperature). For saturated air, the reordering should be applied to a moist-conservative potential temperature, θ m , which is analogous to potential temperature for a dry (subsaturated) atmosphere. Here, θ m is estimated from the Brunt-Väisälä frequency derived by Lalas and Einaudi (1974) in a saturated atmosphere. The application to balloon data shows that the effective turbulent fraction of the troposphere can dramatically increase when saturation is taken into account. Preliminary results of comparisons with data simultaneously collected from the VHF Middle and Upper atmosphere radar (MUR, Japan) seem to give credence to the proposed approach.

Beschreibung: Calibration and validation of the advanced E-Region Wind Interferometer Atmospheric Measurement Techniques Discussions, 5, 8271-8311, 2012 Author(s): S. K. Kristoffersen, W. E. Ward, S. Brown, and J. R. Drummond The advanced E-Region Wind Interferometer (ERWIN II) combines the imaging capabilities of a CCD detector with the wide field associated with field widened Michelson interferometry. This instrument is capable of simultaneous multi-directional wind observations for three different airglow emissions (oxygen green line (O( 1 S)), the P Q(7) and P P(7) emission lines in the O 2 (0–1) atmospheric band and P 1 (3) emission line in the (6,2) hydroxyl Meinel band) on a three minute cadence. In each direction, for 45 s measurements for typical airglow brightness the instrument is capable of line-of-sight wind precisions of ~ 1 m s −1 for hydroxyl and O( 1 S) and ~ 4 m s −1 for O 2 . This precision is achieved using a new data analysis algorithm which takes advantage of the imaging capabilities of the CCD detector along with knowledge of the instrument phase variation as a function of pixel location across the detector. This instrument is currently located in Eureka, Nunavut as part of the Polar Environment Atmospheric Research Laboratory (PEARL). The details of the physical configuration, the data analysis algorithm, the measurement calibration and validation of the observations are described. Field measurements which demonstrate the capabilities of this instrument are presented. To our knowledge, the wind determinations with this instrument are the most accurate and have the highest observational cadence for airglow wind observations of this region of the atmosphere and match the capabilities of other wind measuring techniques.

Beschreibung: Characterisation of GOME-2 formaldehyde retrieval sensitivity Atmospheric Measurement Techniques Discussions, 5, 7095-7139, 2012 Author(s): W. Hewson, H. Bösch, M. P. Barkley, and I. De Smedt Formaldehyde (HCHO) is an important tracer of tropospheric photochemistry, whose slant column abundance can be retrieved from satellite measurements of solar backscattered UV radiation, using differential absorption retrieval techniques. In this work a spectral fitting sensitivity analysis is conducted on HCHO slant columns retrieved from the Global Ozone Monitoring Experiment 2 (GOME-2) instrument. Despite quite different spectral fitting approaches, the retrieved HCHO slant columns have geographic distributions that generally match expected HCHO sources, though the slant column magnitudes and corresponding uncertainties are particularly sensitive to the retrieval set-up. The choice of spectral fitting window, polynomial order, I 0 correction, and inclusion of minor absorbers tend to have the largest impact on the fit residuals. However, application of a reference sector correction using observations over the remote Pacific Ocean, is shown to largely homogenise the resulting HCHO vertical columns, thereby largely reducing any systematic erroneous spectral fitting.

Beschreibung: Feasibility study of using a "travelling" CO 2 and CH 4 instrument to validate continuous in-situ measurement stations Atmospheric Measurement Techniques Discussions, 5, 7141-7185, 2012 Author(s): S. Hammer, G. Konrad, A. T. Vermeulen, O. Laurent, M. Delmotte, A. Jordan, L. Hazan, S. Conil, and I. Levin In the course of the ICOS (Integrated Carbon Observation System)Demo Experiment a feasibility study on the usefulness of a Travelling Comparison Instrument (TCI) was conducted in order to evaluate continuous atmospheric CO 2 and CH 4 measurements at two European stations. The aim of the TCI is to independently measure ambient air in parallel to the standard station instrumentation, thus providing a comprehensive comparison that includes the sample intake system, the instrument itself as well as its calibration and data evaluation. Observed differences between the TCI and the Heidelberg gas chromatographic system, which acted as a reference for the TCI, were −0.02 ± 0.08 μmol mol −1 for CO 2 and −0.3 ± 2.3 nmol mol −1 for CH 4 . Over a period of two weeks each, the continuous CO 2 and CH 4 measurements at two ICOS field stations, Cabauw and OPE, were compared to co-located TCI measurements. At Cabauw mean differences of 0.21 ± 0.06 μmol mol −1 for CO 2 and 0.41 ± 0.50 nmol mol −1 for CH 4 were found. For OPE the mean differences were 0.13 ± 0.07 μmol mol −1 for CO 2 and 0.44 ± 0.36 nmol mol −1 for CH 4 . Potential causes of these observed differences are leakages or contaminations in the intake lines and/or there flushing pumps. At Cabauw station an additional error contribution originates from insufficient flushing of standard gases. Offsets arising from differences in the working standard calibrations or leakages/contaminations in the drying systems are too small to explain the observed differences. Finally a comprehensive quality management strategy for atmospheric monitoring networks is proposed.

Beschreibung: Note on the application of planar-fit rotation for non-omnidirectional sonic anemometers Atmospheric Measurement Techniques Discussions, 5, 7323-7340, 2012 Author(s): M. Li, W. Babel, K. Tanaka, and T. Foken For non-omnidirectional sonic anenometers like the Kaijo-Denki DAT 600 TR61A probe, it is shown that separate planar fit rotations must be used for the undisturbed (open part of the sonic anemometer) and the disturbed sector. This increases the friction velocity while no effect on the scalar fluxes was found. In the disturbed sector, irregular values of − u ′ w ′ 〈 0 were detected for low wind velocities. This study was done for data sets from the Naqu-BJ site on the Tibetan Plateau.

Beschreibung: Aerosol absorption retrieval at ultraviolet wavelengths in a complex environment Atmospheric Measurement Techniques Discussions, 5, 6991-7023, 2012 Author(s): S. Kazadzis, N. Kouremeti, V. Amiridis, A. Arola, and E. Gerasopoulos We have combined sun and sky radiance measurements from a CIMEL sun-photometer and total and diffuse UV irradiance measurements with a multi-filter rotating shadow-band radiometer (UVMFR), in order to calculate aerosol absorption properties (single scattering albedo) in the UV range, for a 10 month period in Athens, Greece. The aerosol extinction optical thickness measured by the CIMEL instrument has been used for the inter-calibration of the UVMFR. The measurements from both instruments were used as input to a radiative transfer model and the single scattering albedo (SSA) for 368 nm and 332 nm has been calculated. The SSA values at these wavelengths, together with synchronous SSA, CIMEL-derived, retrievals at 440 nm, show a mean of 0.88, 0.86 and 0.80, with lowest values (higher absorption) towards lower wavelengths. In addition, noticeable diurnal variations of the SSA in all wavelengths are revealed, with amplitudes in the order of 0.05. Higher SSA wavelength dependence is found for cases of lower Ångström exponents and also an SSA decrease with decreasing extinction optical depth, suggesting an effect of the different aerosol composition.

Beschreibung: Development of a new JMA flask sampling and trace gas measuring system for observation on a cargo aircraft C-130H Atmospheric Measurement Techniques Discussions, 5, 7067-7094, 2012 Author(s): K. Tsuboi, H. Matsueda, Y. Sawa, Y. Niwa, M. Nakamura, D. Kuboike, K. Saito, H. Ohmori, S. Iwatsubo, H. Nishi, Y. Hanamiya, K. Tsuji, and Y. Baba We developed and evaluated a flask air sampling system for atmospheric trace gas observation on a cargo C-130H aircraft, as well as an automated analysis system for the flask samples, as part of a new operational monitoring program of the Japan Meteorological Agency (JMA). Air samples were collected during each flight, between Kanagawa Prefecture (near Tokyo) and Minamitorishima (an island located nearly 2000 km southeast of Tokyo), from the air-conditioning system on the aircraft. The quality assurance test of the flask sampling air was made by specially coordinated flights at a low altitude of 1000 ft over Minamitorishima and comparing the flask values with those obtained at the surface. Based on our storage tests, the flask samples remained stable until analyses. The concentration measuring system for the flask samples has, in addition to the conventional sensors, two laser-based analyzers using wavelength-scanned cavity ring-down spectroscopy (WS-CRDS) and off-axis integrated cavity output spectroscopy (ICOS). Laboratory tests of the measuring system indicated relatively high reproducibility with overall precisions of less than 0.06 ppm for CO 2 , 0.68 ppb for CH 4 , 0.36 ppb for CO, and 0.03 ppb for N 2 O. Inter-comparison experiments for ambient air measurements showed excellent agreements between the laser-based measurement techniques and the conventional methods currently in use. We also found that there are no significant influences of isotope effects for the laser-based analyzers.

Beschreibung: A statistical approach to quantify uncertainty in carbon monoxide measurements at the Izaña global GAW station: 2008–2011 Atmospheric Measurement Techniques Discussions, 5, 6949-6989, 2012 Author(s): A. J. Gomez-Pelaez, R. Ramos, V. Gomez-Trueba, P. C. Novelli, and R. Campo-Hernandez Atmospheric CO in-situ measurements are carried out at the Izaña (Tenerife) global GAW mountain station using a RGA (Reduction Gas Analyser). In-situ measurements at Izaña are representative of the subtropical North-East Atlantic free troposphere, specially during the night period. We present the measurement system configuration, the response function, the calibration scheme, the data processing, the Izaña's 2008–2011 CO nocturnal time series, and the mean diurnal cycle by months. We have developed a rigorous uncertainty analysis for carbon monoxide measurements carried out at the Izaña station which could be applied to other GAW stations. We determine the combined standard uncertainty from four components of the measurement: uncertainty of the WMO standard gases interpolated over the range of measurement, the uncertainty that takes into account the agreement between the standard gases and the response function used, the uncertainty due to the repeatability of the injections, and the propagated uncertainty related to the response function parameters uncertainties (which also takes into account the covariance between the parameters). The mean value of the combined standard uncertainty decreased significantly after March 2009, from 2.37 nmol mol −1 to 1.66 nmol mol −1 , due to improvements in the measurement system. A fifth type of uncertainty we call representation uncertainty is considered when some of the data necessary to compute exactly the mean are absent. Any computed mean has also a propagated uncertainty arising from the uncertainties of the data used to compute the mean. The law of propagation depends on the type of uncertainty component (random or systematic). In-situ hourly means are compared with simultaneous and collocated NOAA flask samples. The uncertainty in the differences is determined and whether these are significant. For 2009–2011, only 24.5% of the differences are significant, and 68% of the differences are between −2.39 and 2.5 nmol mol −1 . Total and annual mean differences are computed using conventional expressions but also expressions with weights based on the minimum variance method. The annual mean differences for 2009–2011 are well within the ±2 nmol mol −1 compatibility goal of GAW.

Beschreibung: Potential of the future thermal infrared space-borne sensor IASI-NG to monitor lower tropospheric ozone Atmospheric Measurement Techniques Discussions, 5, 7025-7065, 2012 Author(s): P. Sellitto, G. Dufour, M. Eremenko, J. Cuesta, P. Dauphin, G. Forêt, B. Gaubert, M. Beekmann, V.-H. Peuch, and J.-M. Flaud The lower tropospheric (LT) ozone concentration is a key factor for air quality (AQ). Observing efficiently LT ozone from space is crucial to monitor and better understand pollution phenomena occurring from inter-continental to local scales, and that have a proven noxious effect on the human health and the biosphere. The Infrared Atmospheric Sounder Interferometer (IASI) flies on MetOp-A spacecraft and is planned to be launched in the next future as part of the other MetOp modules, i.e. MetOp-B and C. IASI has demonstrated to have the capability to single out the LT ozone signal only at favourable conditions, i.e. in presence of high thermal contrast scenarios. New generation satellite instruments are being designed to address several pressing geophysical issues, including a better observation capability of LT ozone. IASI-NG (New Generation), now having reached the accomplishment of design phase-A for launch in the 2020 timeframe as part of the EPS-SG (EUMETSAT Polar System-Second Generation, formerly post-EPS) mission, may render feasible a better observation of AQ in terms of LT ozone. To evaluate the added-value brought by IASI-NG in this context, we developed a pseudo-observation simulator, including a direct simulator of thermal infrared spectra and a full inversion scheme to retrieve ozone concentration profiles. We produced one month (August 2009) of tropospheric ozone pseudo-observations based on both IASI and IASI-NG instrumental configurations. We compared the pseudo-observations and we found a clear improvement of LT ozone (up to 6 km altitude) pseudo-observations quality for IASI-NG. The estimated total error is expected to be more than 35% smaller at 5 km, and 20% smaller for the LT ozone column. The total error on the LT ozone column is, on average, lower than 10% for IASI-NG. IASI-NG is expected to have a significantly better vertical sensitivity (monthly average degrees of freedom surface-6 km of 0.70) and to be sensitive at lower altitudes (more than 0.5 km lower than IASI, reaching values of nearly 3.0 km). Vertical ozone layers of 4 to 5 km thickness are expected to be resolved by IASI-NG, while IASI has a vertical resolution of 6–8 km. According to our analyses, IASI-NG is expected to have the possibility of effectively separate lower from upper tropospheric ozone information even for low sensitivity scenarios. In addition, IASI-NG is expected to be able to better monitor LT ozone patterns at local spatial scale and to monitor abrupt temporal evolutions occurring at time-scales of a few days, thus bringing an expected added-value with respect to IASI for the monitoring of AQ.

Beschreibung: Atmospheric CO 2 , δ(O 2 /N 2 ) and δ 13 CO 2 measurements at Jungfraujoch, Switzerland: results from a flask sampling intercomparison program Atmospheric Measurement Techniques Discussions, 5, 7293-7322, 2012 Author(s): I. T. van der Laan-Luijkx, S. van der Laan, C. Uglietti, M. F. Schibig, R. E. M. Neubert, H. A. J. Meijer, W. A. Brand, A. Jordan, J. M. Richter, M. Rothe, and M. C. Leuenberger We present results from an intercomparison program of CO 2 , δ(O 2 /N 2 ) and δ 13 CO 2 measurements from atmospheric flask samples. Flask samples are collected on a bi-weekly basis at the High Altitude Research Station Jungfraujoch in Switzerland for three European laboratories: the University of Bern, Switzerland, the University of Groningen, the Netherlands and the Max Planck Institute for Biogeochemistry in Jena, Germany. Almost 4 yr of measurements of CO 2 , δ(O 2 /N 2 ) and δ 13 CO 2 are compared in this paper to assess the measurement compatibility of the three laboratories. While the average difference for the CO 2 measurements between the laboratories in Bern and Jena meets the required compatibility goal as defined by the World Meteorological Organisation, the standard deviation of the average differences between all laboratories is not within the required goal. However, the obtained annual trend and seasonalities are the same within their estimated uncertainties. For δ(O 2 /N 2 ) significant differences are observed between the three laboratories. The comparison for δ 13 CO 2 yields the least compatible results and the required goals are not met between the three laboratories. Our study shows the importance of regular intercomparison exercises to identify potential biases between laboratories and the need to improve the quality of atmospheric measurements.

Beschreibung: Long-term greenhouse gas measurements from aircraft Atmospheric Measurement Techniques Discussions, 5, 7341-7382, 2012 Author(s): A. Karion, C. Sweeney, S. Wolter, T. Newberger, H. Chen, A. Andrews, J. Kofler, D. Neff, and P. Tans In March 2009 the NOAA/ESRL/GMD Carbon Cycle and Greenhouse Gases Group collaborated with the US Coast Guard (USCG) to establish the Alaska Coast Guard (ACG) sampling site, a unique addition to NOAA's atmospheric monitoring network. This collaboration takes advantage of USCG bi-weekly Arctic Domain Awareness (ADA) flights, conducted with Hercules C-130 aircraft from March to November each year. NOAA has installed window-replacement inlet plates on two USCG C-130 aircraft and deploys a pallet with NOAA instrumentation on each ADA flight. Flights typically last 8 h and cover a very large area, traveling from Kodiak, AK in the south up to Barrow, AK in the north, and making altitude profiles near the coast as well as in the interior. NOAA instrumentation on each flight includes: a flask sampling system, a continuous CO 2 /CH 4 /CO/H 2 O analyzer, a continuous ozone analyzer, and an ambient temperature and humidity sensor. GPS time and location from the aircraft's navigation system are also collected. Air samples collected in flight are analyzed at NOAA/ESRL for the major greenhouse gases and a variety of halocarbons and hydrocarbons that influence climate, stratospheric ozone, and air quality. Instruments on this aircraft are designed and deployed to be able to collect air samples and data autonomously, so that NOAA personnel visit the site only for installation at the beginning of each season. We present an assessment of the cavity ring-down spectroscopy (CRDS) CO 2 /CH 4 /CO/H 2 O analyzer performance operating on an aircraft over a three-year period. We describe the overall system for making accurate greenhouse gas measurements using a CRDS analyzer on an aircraft with minimal operator interaction. Short and long-term stability of the CRDS analyzer over a seven-month deployment period is better than 0.15 ppm, 2 ppb, and 5 ppb for CO 2 , CH 4 , CO respectively, considering differences of on-board reference tank measurements from a laboratory calibration performed prior to deployment. This stability is not affected by variation in pressure or temperature during flight. Biases and standard deviations of comparisons with flask samples suggest that atmospheric variability, flask-to-flask variability, and possible flask sampling biases may be driving biases in the comparison between flasks and in-situ CRDS measurements.

Beschreibung: Optical property retrievals of subvisual cirrus clouds from OSIRIS limb-scatter measurements Atmospheric Measurement Techniques Discussions, 5, 5313-5355, 2012 Author(s): J. T. Wiensz, D. A. Degenstein, N. D. Lloyd, and A. E. Bourassa We present a technique for retrieving the optical properties of subvisual cirrus clouds detected by OSIRIS, a limb-viewing satellite instrument that measures scattered radiances from the UV to the near-IR. The measurement set is composed of a ratio of limb radiance profiles at two wavelengths that indicates the presence of cloud-scattering regions. Optical properties from an in-situ database are used to simulate scattering by cloud-particles. With appropriate configurations discussed in this paper, the SASKTRAN successive-orders of scatter radiative transfer model is able to simulate accurately the in-cloud radiances from OSIRIS. Configured in this way, the model is used with a multiplicative algebraic reconstruction technique (MART) to retrieve the cloud extinction profile for an assumed effective cloud particle size. The sensitivity of these retrievals to key auxiliary model parameters is shown, and it is demonstrated that the retrieved extinction profile models accurately the measured in-cloud radiances from OSIRIS. Since OSIRIS has an 11-yr record of subvisual cirrus cloud detections, the work described in this manuscript provides a very useful method for providing a long-term global record of the properties of these clouds.

Beschreibung: A method for cloud detection and opacity classification based on ground based sky imagery Atmospheric Measurement Techniques Discussions, 5, 4535-4569, 2012 Author(s): M. S. Ghonima, B. Urquhart, C. W. Chow, J. E. Shields, A. Cazorla, and J. Kleissl Digital images of the sky obtained using a total sky imager (TSI) are classified pixel by pixel into clear sky, optically thin and optically thick clouds. A new classification algorithm was developed that compares the pixel red-blue ratio (RBR) to the RBR of a clear sky library (CSL) generated from images captured on clear days. The difference, rather than the ratio, between pixel RBR and CSL RBR resulted in more accurate cloud classification. High correlation between TSI image RBR and aerosol optical depth (AOD) measured by an AERONET photometer was observed and motivated the addition of a haze correction factor (HCF) to the classification model to account for variations in AOD. Thresholds for clear and thick clouds were chosen based on a training image set and validated with set of manually annotated images. Misclassifications of clear and thick clouds into the opposite category were less than 1%. Thin clouds were classified with an accuracy of 60%. Accurate cloud detection and opacity classification techniques will improve the accuracy of short-term solar power forecasting.

Beschreibung: Global stratospheric aerosol extinction profile retrievals from SCIAMACHY limb-scatter observations Atmospheric Measurement Techniques Discussions, 5, 5993-6035, 2012 Author(s): F. Ernst, C. von Savigny, A. Rozanov, V. Rozanov, K.-U. Eichmann, L. A. Brinkhoff, H. Bovensmann, and J. P. Burrows Stratospheric aerosol extinction profiles are retrieved from SCIAMACHY/Envisat limb-scatter observations in the visible spectral range. The retrieval algorithm is based on a colour-index approach using the normalized limb-radiance profiles at 470 nm and 750 nm wavelength. The optimal estimation approach in combination with the radiative transfer model SCIATRAN is employed for the retrievals. This study presents a detailed description of the retrieval algorithm, and a sensitivity analysis investigating the impact of the most important parameters that affect the aerosol extinction profile retrieval accuracy. It is found that the parameter with the largest impact is surface albedo, particularly for SCIAMACHY observations in the Southern Hemisphere where the error in stratospheric aerosol extinction can be up to 50% if the surface albedo is not well known. The effect of errors in the assumed ozone and neutral density profiles on the aerosol profile retrievals is with generally less than 6% relatively small. The aerosol extinction profiles retrieved from SCIAMACHY are compared with co-located SAGE II solar occultation measurements of stratospheric aerosol extinction during the period 2003–2005. The mean aerosol extinction profiles averaged over all co-locations agree to within 20% between 15 and 35 km altitude. However, larger differences are observed at specific latitudes.

Beschreibung: Long-term continuous atmospheric CO 2 measurements at Baring Head, New Zealand Atmospheric Measurement Techniques Discussions, 5, 5889-5912, 2012 Author(s): G. W. Brailsford, B. B. Stephens, A. J. Gomez, K. Riedel, S. E. Mikaloff Fletcher, S. E. Nichol, and M. R. Manning We present a 39-yr record of continuous atmospheric carbon dioxide (CO 2 ) observations made at Baring Head, New Zealand using a succession of infrared analyser instruments. We include descriptions of the in situ instrumentation, calibration procedures, intercomparison efforts, and data-filtering methods. Located on the southern coast of the North Island, Baring Head is exposed to extended periods of strong air flow from the south with minimal terrestrial influence resulting in low CO 2 variability. The site is therefore well suited for sampling air masses that are representative of the Southern Ocean region. Instrumental precision is better than 0.015 ppm (1-σ) on 1-Hz values and comparisons to over 600 co-located flask samples, as well as laboratory based flask and cylinder comparison exercises, suggests that over recent decades compatibility with respect to the Scripps Institute of Oceanography (SIO) and World Meteorological Organisation (WMO) CO 2 scales has been 0.3 ppm or better.

Beschreibung: Solar Backscatter UV (SBUV) total ozone and profile algorithm Atmospheric Measurement Techniques Discussions, 5, 5913-5951, 2012 Author(s): P. K. Bhartia, R. D. McPeters, L. E. Flynn, S. Taylor, N. A. Kramrova, S. Frith, B. Fisher, and M. DeLand We describe the algorithm that has been applied to develop a 41 yr time series of total ozone and ozone profiles from eight solar-backscatter UV (sbuv) instruments launched on NASA and NOAA satellites since April 1970. Although the basic algorithm is similar to the V8 algorithm that was released about a decade ago and has been in use since then at NOAA, the details of the V8 algorithm have never been published. The current version (V8.6) incorporates several changes including the use of new ozone absorption cross-sections and new ozone and cloud height climatologies. A particular emphasis in this paper is on characterizing the sources of errors that are relevant for deriving trends from monthly mean anomalies and for estimating biases between different types of ozone sensors. We show that variations in the local time of the measurement due to drifting NOAA satellite orbits can complicate the analysis of trends in the upper stratosphere. Such variations not only increase instrumental and algorithmic uncertainties but also require correction for true local time variations of ozone in the upper stratosphere and lower mesosphere for trend analysis. We find that the monthly zonal anomalies derived from the SBUV data have high precision, sufficient to track year-to-year changes in ozone over a broad range of altitudes. However, because of poor vertical resolution the data are less well suited to track short-term variability of ozone at lower altitudes.

Beschreibung: High accuracy measurements of dry mole fractions of carbon dioxide and methane in humid air Atmospheric Measurement Techniques Discussions, 5, 5823-5888, 2012 Author(s): C. W. Rella, H. Chen, A. E. Andrews, A. Filges, C. Gerbig, J. Hatakka, A. Karion, N. L. Miles, S. J. Richardson, M. Steinbacher, C. Sweeney, B. Wastine, and C. Zellweger Traditional techniques for measuring the mole fractions of greenhouse gas in the well-mixed atmosphere have required extremely dry sample gas streams (dew point 〈 −25 °C) to achieve the inter-laboratory compatibility goals set forth by the Global Atmospheric Watch program of the World Meteorological Organization (WMO/GAW) for carbon dioxide (±0.1 ppm) and methane (±2 ppb). Drying the sample gas to low levels of water vapor can be expensive, time-consuming, and/or problematic, especially at remote sites where access is difficult. Recent advances in optical measurement techniques, in particular Cavity Ring Down Spectroscopy (CRDS), have led to the development of highly stable and precise greenhouse gas analyzers capable of highly accurate measurements of carbon dioxide, methane, and water vapor. Unlike many older technologies, which can suffer from significant uncorrected interference from water vapor, these instruments permit for the first time accurate and precise greenhouse gas measurements that can meet the WMO/GAW inter-laboratory compatibility goals without drying the sample gas. In this paper, we present laboratory methodology for empirically deriving the water vapor correction factors, and we summarize a series of in-situ validation experiments comparing the measurements in humid gas streams to well-characterized dry-gas measurements. By using the manufacturer-supplied correction factors, the dry-mole fraction measurements have been demonstrated to be well within the GAW compatibility goals up to at least 1% water vapor. By determining the correction factors for individual instruments once at the start of life, this range can be extended to at least 2% over the life of the instrument, and if the correction factors are determined periodically over time, the evidence suggests that this range can be extended above 4%.

Beschreibung: Cirrus crystal fall velocity estimates using the Match method with ground-based lidars: a first case study Atmospheric Measurement Techniques Discussions, 5, 5787-5822, 2012 Author(s): D. Dionisi, P. Kekchut, C. Hoareau, N. Montoux, and F. Congeduti Cirrus ice particle sedimentation velocity ( v r ) is one of the critical variables for the parameterization of cirrus properties in a global climate model (GCM). In this study a methodology to estimate cirrus properties, such as crystal mean fall speed, through successive lidar measurements is evaluated. This "Match" technique has been applied on cirrus cloud observations and then tested with measurements from two ground-based lidars located in the Mediterranean Area. These systems have similar instrumental characteristics, and are operated manually respectively at the Observatory of Haute Provence (OHP, 43.9° N, 5.7° E) in France and at Rome Tor Vergata (RTV, 41.8° N, 12.6° E) in Italy at a distance of approximately 600 km providing systematic measurements since several years. The both sites are along a typical direction of an air path and a test case of an upper tropospheric cirrus, observed over both sites during the night between 13 and 14 of March 2008, has been identified and investigated. The analysis through lidar primarily parameters (cloud shape and vertical location) reveals a case of a thin sub-visible cirrus (SVC) located around the tropopause. The feasibility to estimate crystal fall velocity has been tested and values of 1.4–1.9 cm s −1 , consistent with simple-shaped small crystals, have been retrieved. Despite several uncertainties that affect the single-wavelength lidar measurements, sedimentation could be a partial reason for the cirrus property changes (e.g. geometrical thickness and back-scattering profile distribution) observed from one site to the other. The backward trajectory analysis suggests a type of cirrus formed by large-scale transport processes (adiabatic cooling of moist air masses coming from the subtropical area around Mexico gulf), which is characterized by a long atmospheric lifetime and horizontal extension of several hundreds of km. This study shows that such approach can be improved in using closer locations, ancillary data (e.g. temperature, water vapour, etc.), particle distribution utilizing multi-wavelengths space-borne lidar measurements or balloon size particle and cirrus microphysical-resolved models.

Beschreibung: Application of linear polarized light for the discrimination of frozen and liquid droplets in ice nucleation experiments Atmospheric Measurement Techniques Discussions, 5, 5753-5785, 2012 Author(s): T. Clauss, A. Kiselev, S. Hartmann, S. Augustin, S. Pfeifer, D. Niedermeier, H. Wex, and F. Stratmann We report on the development and test results of the new optical particle counter TOPS-Ice (Thermostabilized Optical Particle Spectrometer for the detection of Ice particles). The instrument uses measurements of the depolarized component of light scattered by single particles into the near-forward direction (42.5° ± 12.7°) to distinguish between spherical and non-spherical particles. This approach allows the differentiation between liquid water droplets (spherical) and ice particles (non-spherical) having similar volume equivalent sizes and therefore can be used to determine the fraction of frozen droplets in a typical immersion freezing experiment. We show that the numerical simulation of the light scattering on non-spherical particles (ellipsoids in random orientation) with account for the actual scattering geometry used in the instrument supports the validity of the approach, even though the cross polarized component of the light scattered by spherical droplets is not vanishing in this scattering angle. For the separation of the ice particle mode from the liquid droplet mode, we use the width of the pulse detected in the depolarization channel instead of the pulse height. Exploiting the intrinsic relationship between pulse height and pulse width for Gaussian pulses allows us to calculate the fraction of frozen droplets even if the liquid droplet mode dominates the particle ensemble. We present test results obtained with TOPS-Ice in the immersion freezing experiments at the laminar diffusion chamber LACIS (Leipzig Aerosol Cloud Interaction Simulator) and demonstrate the excellent agreement with the data obtained in the same experiment with a different optical instrument. Finally, the advantages of using the cross-polarized light measurements for the differentiation of liquid and frozen droplets in the realistic immersion freezing experiments are discussed.

Beschreibung: The detection of nocturnal N 2 O 5 as HNO 3 by alkali- and aqueous-denuder techniques Atmospheric Measurement Techniques Discussions, 5, 7489-7505, 2012 Author(s): G. J. Phillips, U. Makkonen, G. Schuster, N. Sobanski, H. Hakola, and J. Crowley The almost total anthropogenic control of the nitrogen cycle has led to wide ranging trans-national and national efforts to quantify the effects of reactive nitrogen on the environment. A number of monitoring techniques have been developed for the measurement of nitric acid and subsequent estimation of nitrogen deposition within large networks and for process studies on shorter measurement campaigns. We discuss the likelihood that many of these techniques are sensitive to another important gas-phase component of oxidized nitrogen; dinitrogen pentoxide (N 2 O 5 ). We present measurements using a MARGA wet annular denuder device alongside measurements of N 2 O 5 with a discussion of evidence from the laboratory and the field which suggests that alkali- and aqueous-denuder measurements are sensitive to the sum of HNO 3 + N 2 O 5 . Nocturnal data from these denuder devices should be treated with care before using HNO 3 concentrations derived from these data. This is a systematic error which is highly dependent on ambient conditions and is likely to cause systematic misinterpretation of datasets in periods where N 2 O 5 is significant proportion of NO y . It is also likely that deposition estimates of HNO 3 via data obtained with these methods is compromised to greater or lesser extents depending on the season and environment of the sampling location.

Beschreibung: Measurements of hydrogen cyanide (HCN) and acetylene (C 2 H 2 ) from the Infrared Atmospheric Sounding Interferometer (IASI) Atmospheric Measurement Techniques Discussions, 5, 7567-7586, 2012 Author(s): V. Duflot, D. Hurtmans, L. Clarisse, Y. R'honi, C. Vigouroux, M. De Mazière, E. Mahieu, C. Servais, C. Clerbaux, and P.-F. Coheur Hydrogen cyanide (HCN) and acetylene (C 2 H 2 ) are ubiquitous atmospheric trace gases with medium lifetime, which are frequently used as indicators of combustion sources and as tracers for atmospheric transport and chemistry. Because of their weak infrared absorption, overlapped by the CO 2 Q -branch near 720 cm −1 , nadir sounders have up to now failed to measure these gases routinely. Taking into account CO 2 line mixing we provide for the first time extensive measurements of HCN and C 2 H 2 total columns at Reunion Island (21° S; 55° E) and Jungfraujoch (46° N; 8° E) in 2009–2010 using observations from the Infrared Atmospheric Sounding Interferometer (IASI). These are compared with local ground-based Fourier Transform InfraRed (FTIR) measurements and we demonstrate that the seasonality is well captured, except for HCN at Jungfraujoch. We also examine a nonspecific biomass burning plume over austral Africa and show that the emission ratios with respect to CO agree with previously reported values.

Beschreibung: Climatology of aerosol optical properties in Northern Norway and Svalbard Atmospheric Measurement Techniques Discussions, 5, 7619-7640, 2012 Author(s): Y.-C. Chen, B. Hamre, Ø Frette, and J. J. Stamnes We present comparisons between estimates of the aerosol optical thickness and the Ångström exponent in Northern Norway and Svalbard based on data from AERONET stations at Andenes (69° N, 16° E, 379 m altitude) and Hornsund (77° N, 15° E, 10 m altitude) for the period 2008–2010. The three-year annual mean values for the aerosol optical thickness at 500 nm τ (500) at Andenes and Hornsund were 0.11 and 0.10, respectively. At Hornsund, there was less variation of the monthly mean value of τ (500) than at Andenes. The annual mean values of the Ångström exponent α at Andenes and Hornsund were 1.18 and 1.37, respectively. At Andenes and Hornsund α was found to be larger than 1.0 in 68% and 93% of the observations, respectively, indicating that fine-mode particles were dominating at both sites. Both sites had a similar seasonal variation of the aerosol size distribution although one site is in an Arctic area while the other site is in a sub-arctic area.

Beschreibung: Critical evaluation of the MODIS Deep Blue aerosol optical depth product for data assimilation over North Africa Atmospheric Measurement Techniques Discussions, 5, 7815-7865, 2012 Author(s): Y. Shi, J. Zhang, J. S. Reid, E. J. Hyer, and N. C. Hsu A total of eight years of Terra (2000–2007) and Aqua (2002–2009) Moderate Resolution Imaging Spectroradiometer (MODIS) Deep Blue (DB) collection 5.1 (c5.1) data were examined for their potential usage in aerosol assimilation. Uncertainties in the DB Aerosol Optical Depth (AOD) were identified and studied. Empirical corrections and quality assurance procedures were developed for North Africa and the Arabian Peninsula. After applying quality assurance and quality check procedures, the Root-Mean-Square-Error (RMSE) in the MODIS Terra and Aqua AOD are reduced by 18.1 and 18.2% to 0.16 and 0.17, respectively, with respect to AERONET data. These procedures were also applied to two months of DB collection 6 (c6) AOD data and reductions in RMSE were found, indicating that the algorithms developed for c5.1 data are applicable to c6 data to some extent. A new quality-assured DB level 3 AOD product was developed for future implementations in both aerosol data assimilation and climate related applications.

Beschreibung: Aerosol information content analysis of multi-angle high spectral resolution measurements and its benefit for high accuracy greenhouse gas retrievals Atmospheric Measurement Techniques Discussions, 5, 2857-2885, 2012 Author(s): C. Frankenberg, O. Hasekamp, C. O'Dell, S. Sanghavi, A. Butz, and J. Worden New generations of space-borne spectrometers for the retrieval of atmospheric abundances of greenhouse gases require unprecedented accuracies as atmospheric variability of long-lived gases is very low. These instruments, such as GOSAT and OCO-2, typically use a high spectral resolution oxygen channel (O 2 A-band) in addition to CO 2 and CH 4 channels to discriminate changes in the photon path-length distribution from actual trace gas amount changes. Inaccurate knowledge of the photon path-length distribution, determined by scatterers in the atmosphere, is the prime source of systematic biases in the retrieval. In this paper, we investigate the combined aerosol and greenhouse gas retrieval using multiple satellite viewing angles simultaneously. We find that this method, hitherto only applied in multi-angle imagery such as from MISR, greatly enhances the ability to retrieve aerosol properties by 2–3 degrees of freedom. We find that the improved capability to retrieve aerosol parameters significantly reduces interference errors introduced into retrieved CO 2 and CH 4 total column averages. Instead of focussing solely on improvements in spectral and spatial resolution, signal-to-noise ratios or sampling frequency, multiple angles reduce uncertainty in space based greenhouse gas retrievals more effectively and provide a new potential for dedicated aerosols retrievals.

Beschreibung: Evaluation of continuous water vapor δD and δ 18 O measurements by off-axis integrated cavity output spectroscopy Atmospheric Measurement Techniques Discussions, 5, 2821-2855, 2012 Author(s): N. Kurita, B. D. Newman, L. J. Araguas-Araguas, and P. Aggarwal Recent commercially available laser spectroscopy systems enabled us to continuously and reliably measure the δD and δ 18 O of atmospheric water vapor. The use of this new technology is becoming popular because of its advantages over the conventional approach based on cold trap collection. These advantages include much higher temporal resolution/continuous monitoring and the ability to make direct measurements of both isotopes in the field. Here, we evaluate the accuracy and precision of the laser based water vapor isotope instrument through a comparison of measurements with those found using the conventional cold trap method. A commercially available water vapor isotope analyzer (WVIA) with the vaporization system of a liquid water standard (Water Vapor Isotope Standard Source, WVISS) from Los Gatos Research (LGR) Inc. was used for this study. We found that the WVIA instrument can provide accurate results if: (1) correction is applied for time-dependent isotope drift, (2) normalization to the VSMOW/SLAP scale is implemented, and (3) the water vapor concentration dependence of the isotopic ratio is also corrected. In addition, since the isotopic value of water vapor generated by the WVISS is also dependent on the concentration of water vapor, this effect must be considered to determine the true water vapor concentration effect on the resulting isotope measurement. To test our calibration procedure, continuous water vapor isotope measurements using both a laser instrument and a cold trap system were carried out at the IAEA Isotope Hydrology Laboratory in Vienna from August to December 2011. The calibrated isotopic values measured using the WVIA agree well with those obtained via the cold trap method. The standard deviation of the isotopic difference between both methods is about 1.4‰ for δD and 0.28‰ for δ 18 O. This precision allowed us to obtain reliable values for d -excess. The day-to-day variation of d -excess measured by WVIA also agrees well with that found using the cold trap method. These results demonstrate that a coupled system, using commercially available WVIA and WVISS instruments can provide continuous and accurate isotope data, with results achieved similar to those obtained using the conventional method, but with drastically improved temporal resolution.

Beschreibung: A disjunct eddy accumulation system for the measurement of BVOC fluxes: instrument characterizations and field deployment Atmospheric Measurement Techniques Discussions, 5, 2703-2746, 2012 Author(s): G. D. Edwards, D. K. Martins, T. Starn, K. Pratt, and P. B. Shepson Biological volatile organic compounds (BVOCs), such as isoprene and monoterpenes, are emitted in large amounts from forests. Quantification of the flux of BVOCs is critical in the evaluation of the impact of these compounds on the concentrations of atmospheric oxidants and on the production of secondary organic aerosol. A disjunct eddy accumulation (DEA) sampler system was constructed for the measurement of speciated BVOC fluxes. Unlike traditional eddy covariance (EC), the relatively new technique of disjunct sampling differs by taking short, discrete samples that allows for slower sampling frequencies. Disjunct sample airflow is directed into cartridges containing sorbent materials at sampling rates proportional to the magnitude of the vertical wind. Compounds accumulated on the cartridges are then quantified by thermal desorption and gas chromatography. Herein, we describe our initial tests to evaluate the disjunct sampler including the application of using vertical wind measurements to create optimized sampling thresholds. Measurements of BVOC fluxes obtained from DEA during its deployment above a mixed hardwood forest at the University of Michigan Biological Station (Pellston, MI) during the 2009 CABINEX field campaign are reported. Daytime (09:00 a.m. to 05:00 p.m.) isoprene fluxes, when averaged over the footprint of the tower were 1.31 mg m −2 h −1 which is comparable to previous flux measurements at this location. Speciated monoterpene fluxes are some of the first to be reported from this site. Daytime averages were 26.7 μg m −2 h −1 for α-pinene and 10.6 μg m −2 h −1 for β-pinene. These measured concentrations and fluxes were compared to the output of an atmospheric chemistry model, and were found to be consistent with our knowledge of the variables that control BVOCs fluxes at this site.

Beschreibung: Carbon monoxide measurements onboard the CARIBIC passenger aircraft using UV resonance fluorescence Atmospheric Measurement Techniques Discussions, 5, 2681-2702, 2012 Author(s): D. Scharffe, F. Slemr, C. A. M. Brenninkmejer, and A. Zahn Goal of the project CARIBIC (Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrumented Container) is to carry out regular and detailed observations of atmospheric composition (particles and gases) at cruising altitudes of passenger aircraft, i.e., at 9–12 km. Continuous, fast measurement of CO is indispensable for the chemical characterization of encountered air masses, for the detection of plumes of polluted air and for studying troposphere-stratosphere transport. CO is measured by a commercial resonance fluorescence UV instrument modified for the use onboard passenger aircraft. Modifications were necessary to optimize the instrument reliability allowing unattended operation for several days. The instrument has a precision of 1–2 ppbv at an integration time of 1 s. The response time to reach 66.6% signal strength is 2 s. We describe the modifications of the instrument, the experiences made during its operation since December 2004, the quality control of CO measurements onboard CARIBIC, and suggest a regular service routine that guarantees long-term high-quality data.

Beschreibung: Implications of satellite swath width on global aerosol optical thickness statistics Atmospheric Measurement Techniques Discussions, 5, 2795-2820, 2012 Author(s): P. R. Colarco, L. A. Remer, R. A. Kahn, R. C. Levy, and E. J. Welton We assess the impact of swath width on the statistics of aerosol optical thickness (AOT) retrieved by satellite, as inferred from observations made by the Moderate Resolution Imaging Spectroradiometer (MODIS). Using collocated AERONET sun photometer observations we develop a correction to the MODIS data to account for calibration and algorithmic view angle dependency in the retrieved AOT. We sub-sample and correct the AOT data from the MODIS Aqua instrument along several candidate swaths of various widths for the years 2003–2011. We find that over ocean the global, annual mean AOT is within ± 0.01 of the full swath AOT for all of our sub-samples. Over land, however, most of our sub-samples are outside of this criterion range in the global, annual mean. Moreover, at smaller spatial and temporal scales we find wide deviation in the sub-sample AOT relative to the full swath over both land and ocean. In all, the sub-sample AOT is within ± 0.01 of the full swath value less than 25% of the time over land, and less than 50% of the time over ocean (less than 35% for all but the widest of our sub-sample swaths). These results suggest that future aerosol satellite missions having only narrow swath views may not sample the true AOT distribution sufficiently to reduce significantly the uncertainty in aerosol direct forcing of climate.

Beschreibung: Evaluating nighttime CALIOP 0.532 μm aerosol optical depth and extinction coefficient retrievals Atmospheric Measurement Techniques Discussions, 5, 2747-2794, 2012 Author(s): J. R. Campbell, J. L. Tackett, J. S. Reid, J. Zhang, C. A. Curtis, E. J. Hyer, W. R. Sessions, D. L. Westphal, J. M. Prospero, E. J. Welton, A. H. Omar, M. A. Vaughan, and D. M. Winker NASA Cloud Aerosol Lidar with Orthogonal Polarization (CALIOP) Version 3.01 5-km nighttime 0.532 μm aerosol optical depth (AOD) datasets from 2007 are screened, averaged and evaluated at 1° × 1° resolution versus corresponding/co-incident 0.550 μm AOD derived using the US Navy Aerosol Analysis and Prediction System (NAAPS), featuring two-dimensional variational assimilation of quality-assured NASA Moderate Resolution Imaging Spectroradiometer (MODIS) and Multi-angle Imaging Spectroradiometer (MISR) AOD. Daytime datasets are investigated similarly for context. Regional-mean CALIOP vertical profiles of night/day 0.532 μm extinction coefficient are compared with 0.523/0.532 μm ground-based lidar measurements to investigate representativeness and diurnal variability. In this analysis, mean nighttime CALIOP AOD are mostly lower than daytime (0.121 vs. 0.126 for all aggregated data points, and 0.099 vs. 0.102 when averaged globally per normalized 1° × 1° bin), though the relationship is reversed over land and coastal regions when the data are averaged per normalized bin (0.134/0.108 vs. 0140/0.112, respectively). Offsets assessed within single bins alone approach ±20%. CALIOP AOD, both day and night, are higher than NAAPS over land (0.137 vs. 0.124) and equal over water (0.082 vs. 0.083) when averaged globally per normalized bin. However, for all data points inclusive, NAAPS exceeds CALIOP over land, coast and ocean, both day and night. Again, differences assessed within single bins approach 50% in extreme cases. Correlation between CALIOP and NAAPS AOD is comparable during both day and night. Higher correlation is found nearest the equator, both as a function of sample size and relative signal magnitudes inherent at these latitudes. Root mean square deviation between CALIOP and NAAPS varies between 0.1 and 0.3 globally during both day/night. Averaging of CALIOP along-track AOD data points within a single NAAPS grid bin improves correlation and RMSD, though day/night and land/ocean biases persist and are believed systematic. Vertical profiles of extinction coefficient derived in the Caribbean compare well with ground-based lidar observations, though potentially anomalous selection of a-priori lidar ratios for CALIOP retrievals is likely inducing some discrepancies. Mean effective aerosol layer top heights are stable between day and night, indicating consistent layer-identification diurnally, which is noteworthy considering the potential limiting effects of ambient solar noise during day.

Beschreibung: Systematic and rapid extraction of direct downwelling irradiance estimates from Campbell-Stokes sunshine recorder archives Atmospheric Measurement Techniques Discussions, 5, 8729-8757, 2012 Author(s): A. M. Horseman, T. Richardson, A. T. Boardman, W. Tych, R. Timmis, and A. R. MacKenzie An improved, semi-automatic method for analysing the cards from the widely used Campbell-Stokes sunshine recorder is described. We show how the application of inexpensive commercial equipment and practices can simply and robustly build an archive of high-quality card images and manipulate them into a form suitable for easy further analysis. Rectified and registered digital images are produced, with the card's midday marker in the middle of the longest side, and with a temporal scaling of 150 px h −1 . The method improves on previous, mostly manual, analyses by simplifying and automating steps into a process capable of handling thousands of cards in a practical time-scale. A prototype method of extraction of data from this archive is then tested by comparison with records from a co-located pyrheliometer at a resolution of the order of minutes. The comparison demonstrates that the Campbell-Stokes recorder archive contains a time series of downwelling solar-irradiance-related data with similar characteristics to that of benchmark pyrheliometer data from the baseline solar radiation network. A universal transfer function for card burn to direct downwelling short-wave radiation is still some way off and is the subject of ongoing research. Until such time as a universal transfer function is available, specific functions for extracting data in particular circumstances offer a useful way forward. The new image-capture method offers a practical way to exploit the worldwide sets of long-term Campbell-Stokes recorder data to create a time series of solar irradiance and atmospheric aerosol loading metrics reaching back over 100 yr from the present day.

Beschreibung: Retrieval of aerosol microphysical and optical properties above liquid clouds from POLDER/PARASOL polarization measurements Atmospheric Measurement Techniques Discussions, 5, 6083-6145, 2012 Author(s): F. Waquet, C. Cornet, J.-L. Deuzé, O. Dubovik, F. Ducos, P. Goloub, M. Herman, T. Lapionak, L. Labonnote, J. Riedi, D. Tanré, F. Thieuleux, and C. Vanbauce Most of the current aerosol retrievals from passive sensors are restricted to cloud-free scenes, which strongly reduces our ability to monitor the aerosol properties at a global scale. The presence of Aerosols Above Clouds (AAC) affects the polarized light reflected by the cloud layer, as shown by the spaceborne measurements provided by the POlarization and Directionality of Earth Reflectances (POLDER) instrument. We present new developments that allow retrieving the properties of mineral dust particles when they are present above clouds. These particles do not much polarize light but strongly attenuate the polarized cloud bow generated by the beneath liquid cloud layer. The spectral attenuation can be used to qualitatively identify the nature of the particles (i.e. mineral dust particles or biomass burning aerosols) whereas the magnitude of the attenuation is related to the optical thickness of the aerosol layer. We provide accurate polarized radiance calculations for AAC scenes and evaluate the contribution of the POLDER polarization measurements for the simultaneous retrieval of the aerosol and clouds properties. We investigate various scenes with mineral dust particles and biomass burning aerosols above clouds. We found that the magnitude of the primary cloud bow cannot be accurately estimated with a plane parallel transfer radiative code. The errors for the modelling of the polarized cloud bow are between 5 and 8% for homogenous cloudy scenes, as shown by a 3-D radiative transfer code. For clouds, our results confirm that the droplets size distribution is narrow in high latitude ocean regions and that the droplets effective radii retrieved from polarization measurements and from total radiance measurements are generally close for AAC scenes (departures smaller than 2 μm). For the aerosols, the POLDER polarization measurements are primarily sensitive to the particles load, size distribution, shape and real refractive index. An algorithm was developed to retrieve the Aerosol Optical Thickness (AOT) and the Angström exponent above clouds in an operational way. This method was applied to various regions of the world and time period. Large mean AOTs above clouds at 0.865 μm (〉0.3) are retrieved for oceanic regions near the coasts of South Africa and California (〉0.1) that correspond to biomass burning aerosols whereas even larger mean AOTs above clouds for mineral dust particles (〉0.6) are also retrieved near the coasts of Senegal (for June–August 2008). For these regions and time period, the direct AAC radiative forcing is likely to be significant. The final aim of this work is the global monitoring of the aerosol above clouds properties and the estimation of the direct aerosol radiative forcing in cloudy scenes.

Beschreibung: Online atmospheric pressure chemical ionization ion trap mass spectrometry (APCI-IT-MS n ) for measuring organic acids in concentrated bulk aerosol – a laboratory and field study Atmospheric Measurement Techniques Discussions, 5, 6147-6182, 2012 Author(s): A. L. Vogel, M. Äijälä, M. Brüggemann, M. Ehn, H. Junninen, T. Petäjä, D. R. Worsnop, M. Kulmala, J. Williams, and T. Hoffmann The field application of an aerosol concentrator in conjunction with an atmospheric pressure chemical ionization ion trap mass spectrometer (APCI-IT-MS) at the boreal forest station SMEAR II at Hyytiälä, Finland, is demonstrated in this study. APCI is a soft ionization technique allowing online measurements of organic acids in the gas and particle phase. The detection limit for the acid species in the particle phase was increased by a factor of 7.5 to 11 (e.g. ~40 ng m −3 for pinonic acid) by using the miniature Versatile Aerosol Concentration Enrichment System (mVACES) upstream of the mass spectrometer. The APCI-IT-MS was calibrated in the negative ion mode with two biogenic organic acid standards – pinic acid and pinonic acid. Pinic acid was used as a surrogate for the quantification of the total amount of organic acids in the ambient aerosol based on the total signal intensities in the negative ion mode. The results were compared with the total organic signal of a C-ToF-AMS during the HUMPPA-COPEC 2010 field campaign. The campaign average contribution of organic acids measured by APCI-IT-MS to the total sub-micron organic aerosol mass was estimated to be about 60%. Very good correlation between APCI-IT-MS and C-ToF-AMS (Pearson's R = 0.94) demonstrates soft ionization mass spectrometry as a complimentary technique to AMS with electron impact ionization. MS 2 studies of specific m/z ratios recorded during the HUMPPA-COPEC 2010 field campaign were compared to MS 2 studies of selected monoterpene oxidation products formed in simulation chamber experiments. The comparison of the resulting fragments shows that oxidation products of the main VOCs emitted at Hyytiälä (α-pinene and Δ 3 -carene) cannot account for all of the measured fragments, which illustrates the complexity of ambient aerosol and possibly indicates unidentified or underestimated biogenic SOA precursor in the boreal forest.

Beschreibung: Using particle filter to track horizontal variations of atmospheric duct structure from radar sea clutter Atmospheric Measurement Techniques Discussions, 5, 6059-6082, 2012 Author(s): X. F. Zhao and S. X. Huang This paper addresses the problem of estimating range-varying parameters of the height-dependent refractivity over the sea surface from radar sea clutter. In the forward simulation, the split-step Fourier parabolic equation (PE) is used to compute the radar clutter power in the complex refractive environments. Making use of the inherent Markovian structure of the split-step Fourier PE solution, the refractivity from clutter (RFC) problem is formulated within a nonlinear recursive Bayesian state estimation framework. Particle filter (PF) that is a technique for implementing a recursive Bayesian filter by Monte Carlo simulations is used to track range-varying characteristics of the refractivity profiles. Basic ideas of employing PF to solve RFC problem are introduced. Both simulation and real data results are presented to check up the feasibility of PF-RFC performances.

Beschreibung: Evaluation of a cavity ring-down spectrometer for in-situ observations of 13 CO 2 Atmospheric Measurement Techniques Discussions, 5, 6037-6058, 2012 Author(s): F. R. Vogel, L. Huang, D. Ernst, L. Giroux, S. Racki, and D. E. J. Worthy With the emergence of wide-spread application of cavity ring-down spectrometers (CRDS) to monitor δ 13 C in atmospheric CO 2 there is a growing need to ensure well calibrated measurements. We characterized a cavity ring-down spectrometer system used for continuous in-situ monitoring of atmospheric 13 CO 2 . We found no concentration dependency of the δ 13 C ratio within the range of 303–437 ppm. We designed a calibration scheme according to the diagnosed instrumental drifts and established a quality assurance protocol. We find that the repeatability of 10 min measurements is 0.25‰ and 0.15‰ for 20 min integrated averages. We found the cross-sensitivity to C 4 in the samples to be 0.42 ± 0.02‰ ppm −1 . Our ongoing target measurements yield standard deviations of 0.26–0.28‰ for 10 min averages. We furthermore estimate the reproducibility of the system for ambient air samples from weekly measurements of a long-term target gas to be 0.18‰. We find only a miniscule offset of 0.002 ± 0.025‰ of the CRDS and Environment Canada's isotope ratio mass spectrometer (IRMS) results for four target gases used over the course of one year.

Beschreibung: The effect of hygroscopicity on sea-spray aerosol fluxes: a comparison of high-rate and bulk correction methods Atmospheric Measurement Techniques Discussions, 5, 6285-6321, 2012 Author(s): D. A. J. Sproson, I. M. Brooks, and S. J. Norris The eddy covariance technique is the most direct of the methods that have been used to measure the flux of sea-spray aerosol between the ocean and atmosphere, but has been applied in only a handful of studies. However, unless the aerosol is dried before the eddy covariance measurements are made, the hygroscopic nature of sea-spray may combine with a relative humidity flux to result in a bias in the calculated aerosol flux. "Bulk" methods have been presented to account for this bias, however they rely on assumptions of the shape of the aerosol spectra which may not be valid for near-surface measurements of sea-spray. Here we describe a method of correcting aerosol spectra for relative humidity induced size variations at the high frequency (10 Hz) measurement timescale, where counting statistics are poor and the spectral shape cannot be well represented by a simple power law. Such a correction allows the effects of hygroscopicity and relative humidity flux on the aerosol flux to be explicitly evaluated and compared to the bulk corrections, both in their original form and once reformulated to better represent the measured mean aerosol spectra. In general, the bulk corrections – particularly when reformulated for the measured mean aerosol spectra – perform relatively well, producing flux corrections of the right sign and approximate magnitude. However, there are times when the bulk methods either significantly over- or underestimate the required flux correction. We thus conclude that, where possible, relative humidity corrections should be made at the measurement frequency.

Beschreibung: On the absolute calibration of SO 2 cameras Atmospheric Measurement Techniques Discussions, 5, 6183-6240, 2012 Author(s): P. Lübcke, N. Bobrowski, S. Illing, C. Kern, J. M. Alvarez Nieves, L. Vogel, J. Zielcke, H. Delgado Granados, and U. Platt Sulphur dioxide emission flux measurements are an important tool for volcanic monitoring and eruption risk assessment. The SO 2 camera technique remotely measures volcanic emissions by analysing the ultraviolet absorption of SO 2 in a narrow spectral window between 305 nm and 320 nm using solar radiation scattered in the atmosphere. The SO 2 absorption is selectively detected by mounting band-pass interference filters in front of a two-dimensional, UV-sensitive CCD detector. While this approach is simple and delivers valuable insights into the two-dimensional SO 2 distribution, absolute calibration has proven to be difficult. An accurate calibration of the SO 2 camera (i.e., conversion from optical density to SO 2 column density, CD) is crucial to obtain correct SO 2 CDs and flux measurements that are comparable to other measurement techniques and can be used for volcanological applications. The most common approach for calibrating SO 2 camera measurements is based on inserting quartz cells (cuvettes) containing known amounts of SO 2 into the light path. It has been found, however, that reflections from the windows of the calibration cell can considerably affect the signal measured by the camera. Another possibility for calibration relies on performing simultaneous measurements in a small area of the camera's field-of-view (FOV) by a narrow-field-of-view Differential Optical Absorption Spectroscopy (NFOV-DOAS) system. This procedure combines the very good spatial and temporal resolution of the SO 2 camera technique with the more accurate column densities obtainable from DOAS measurements. This work investigates the uncertainty of results gained through the two commonly used, but quite different calibration methods (DOAS and calibration cells). Measurements with three different instruments, an SO 2 camera, a NFOV-DOAS system and an Imaging DOAS (IDOAS), are presented. We compare the calibration-cell approach with the calibration from the NFOV-DOAS system. The respective results are compared with measurements from an IDOAS to verify the calibration curve over the spatial extend of the image. Our results show that calibration cells can lead to an overestimation of the SO 2 CD by up to 60% compared with CDs from the DOAS measurements. Besides these errors of calibration, radiative transfer effects (e.g. light dilution, multiple scattering) can significantly influence the results of both instrument types. These effects can lead to an even more significant overestimation or, depending on the measurement conditions, an underestimation of the true CD. Previous investigations found that possible errors can be more than an order of magnitude. However, the spectral information from the DOAS measurements allows to correct for these radiative transfer effects. The measurement presented in this work were taken at Popocatépetl, Mexico, between 1 March 2011 and 4 March 2011. Average SO 2 emission rates between 4.00 kg s −1 and 14.34 kg s −1 were observed.

Beschreibung: MAX-DOAS observations of the total atmospheric water vapour column and comparison with independent observations Atmospheric Measurement Techniques Discussions, 5, 6241-6283, 2012 Author(s): T. Wagner, M. O. Andreae, S. Beirle, S. Dörner, K. Mies, and R. Shaiganfar We developed an algorithm for the retrieval of the atmospheric water vapour column from Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) observations in the yellow and red spectral range. The retrieval is based on the so called geometric approximation and does not depend on a-priori information, extensive radiative transfer simulations, or the construction of large look-up tables. Disturbances of the radiative transfer due to aerosols and clouds are simply corrected using the simultaneously measured absorptions of the oxygen dimer, O 4 . We applied our algorithm to MAX-DOAS observations made at the Max Planck Institute for Chemistry in Mainz, Germany, from March to August 2011 and compared the results to independent observations. Good agreement with Aerosol Robotic Network (AERONET) and European Centre for Medium-Range Weather Forecasting (ECMWF) H 2 O vertical column densities (VCDs) is found, while the agreement with satellite observations is less good, most probably caused by the shielding effect of clouds for the satellite observations. Good agreement is also found with near-surface in-situ observations, and it was possible to derive average daily H 2 O layer heights (between 1.5 km and 3 km). MAX-DOAS measurements use cheap and simple instrumentation and can be run automatically. One important advantage of our algorithm is that the H 2 O VCD can be retrieved even under cloudy conditions (except clouds with very high optical thickness).

Beschreibung: Emission-factor uncertainties in maritime transport in the Strait of Gibraltar, Spain Atmospheric Measurement Techniques Discussions, 5, 5953-5991, 2012 Author(s): J. Moreno-Gutiérrez, V. Durán-Grados, Z. Uriondo, and J. Ángel Llamas A reliable and up-to-date maritime emission inventory is essential for atmospheric scientists quantifying the impact of shipping. The objective of this study is to estimate the atmospheric emissions of SO 2 , NO x , CO 2 and PM 10 by international merchant shipping in 2007 in the Strait of Gibraltar, Spain, including the Algeciras Bay by two methods. Two methods (both bottom-up) have been used in this study: 1. Establishing engine power-based emission factors (g kWh −1 , EPA) or the mass of pollutant per work performed by the engine for each of the relevant components of the exhaust gas from diesel engines and power for each ship. 2. Establishing fuel-based emission factors (kg emitted/t of fuel) or mass of pollutant per mass of combusted fuel for each of the relevant components of the exhaust gas and a fuel-consumption inventory (IMO). In both methods, the means to estimate engine power and fuel-consumption inventories are the same. The exhaust from boilers and incinerators is regarded as a small contributor and excluded. In total, an estimated average of 1 389 111.05 t of CO 2 , 23 083.09 t of SO 2 , 32 005.63 t of NO x and 2972 t of PM 10 were emitted from January 2007 until December 2007 by international and domestic shipping. The estimated total fuel consumption amounts to 437 405.84 t. The major differences between the estimates generated by the two methods are for NO x (16% in certain cases) and CO (up to 23%). A total difference for all compounds of 3038 t (approximately 2%) has been found between the two methods but it is not areasonable estimate of uncertainty. Therefore, the results for both methods may be considered acceptable because the actual uncontrolled deviations appear in the changes in emission factors that occur for a given engine with age. These deviations are often difficult to quantify and depend on individual shipboard service and maintenance routines. Emission factors for CO and NO x are not constant and depend on engine condition. For example, tests conducted by the authors of this paper demonstrate that when an engine operates under normal in-service conditions, the emissions are within limits. However, with a small fault in injection timing, the NO x emission exceeds the limits (30% higher value in some cases). A fault in the maintenance of the injection nozzles increases the CO emission (15% higher value in some cases).

Beschreibung: First middle-atmospheric zonal wind profile measurements with a new ground-based microwave Doppler-spectro-radiometer Atmospheric Measurement Techniques Discussions, 5, 5107-5149, 2012 Author(s): R. Rüfenacht, N. Kämpfer, and A. Murk We report on the wind radiometer WIRA, a new ground-based microwave Doppler-spectro-radiometer specifically designed for the measurement of middle-atmospheric horizontal wind by observing ozone emission spectra at 142.17504 GHz. Currently, wind speeds in five levels between 30 and 79 km can be retrieved what makes WIRA the first instrument able to continuously measure horizontal wind in this altitude range. For an integration time of one day the measurement error on each level lies at around 25 m s −1 . With a planned upgrade this value is expected to be reduced by a factor of 2 in the near future. On the altitude levels where our measurement can be compared to wind data from the European Centre for Medium-Range Weather Forecasts (ECMWF) very good agreement in the long-term statistics as well as in short time structures with a duration of a few days has been found. WIRA uses a passive double sideband heterodyne receiver together with a digital Fourier transform spectrometer for the data acquisition. A big advantage of the radiometric approach is that such instruments can also operate under adverse weather conditions and thus provide a continuous time series for the given location. The optics enables the instrument to scan a wide range of azimuth angles including the directions east, west, north, and south for zonal and meridional wind measurements. The design of the radiometer is fairly compact and its calibration does not rely on liquid nitrogen what makes it transportable and suitable for campaign use. WIRA is conceived in a way that it can be operated remotely and does hardly require any maintenance. In the present paper, a description of the instrument is given, and the used techniques for the wind retrieval based on the determination of the Doppler shift of the measured atmospheric ozone emission spectra are outlined. Their reliability was tested using MonteCarlo simulations. Finally, a first time series of 11 months of zonal wind measurements over Bern (46°57' N, 7°26' E) is presented and compared to ECMWF wind data.

Beschreibung: Combined wind measurements by two different lidar instruments in the Arctic middle atmosphere Atmospheric Measurement Techniques Discussions, 5, 4123-4156, 2012 Author(s): J. Hildebrand, G. Baumgarten, J. Fiedler, U.-P. Hoppe, B. Kaifler, F.-J. Lübken, and B. P. Williams During a joint campaign in January 2009 the Rayleigh/Mie/Raman (RMR) lidar and the sodium lidar at the ALOMAR Observatory (69° N, 16° E) in Northern Norway were operated simultaneously for more than 40 h, collecting data for wind measurements in the middle atmosphere from 30 up to 110 km altitude. At the upper (lower) altitude range where the RMR (sodium) lidar can operate, both lidars probe the same sounding volume, allowing to compare the derived wind speeds. We present the first simultaneous common volume wind measurements in the middle atmosphere using two different lidar instruments. The comparison of winds derived by RMR and sodium lidar is excellent for long integration times of 10 h as well as shorter ones of 1 h. Combination of data from both lidars allows identifying wavy structures between 30 and 110 km altitude, whose amplitudes increase with height. We have also performed lidar measurements of the same wind component using two independent branches of the RMR lidar and found a good agreement of the results but also identified inhomogeneities in the horizontal wind at about 55 km altitude of up to 20 ms −1 . Such small scale inhomogeneities in the horizontal wind field are an essential challenge when comparing data from different instruments.

Beschreibung: A new disjunct eddy-covariance system for BVOC flux measurements – validation on CO 2 and H 2 O fluxes Atmospheric Measurement Techniques Discussions, 5, 4157-4193, 2012 Author(s): R. Baghi, P. Durand, C. Jambert, C. Jarnot, C. Delon, D. Serça, N. Striebig, M. Ferlicoq, and P. Keravec The disjunct eddy covariance (DEC) method is an interesting alternative to the conventional eddy covariance (EC) method, because it allows the estimation of turbulent fluxes of species for which fast sensors are not available. A new disjunct sampling system (called MEDEE) was developed and validated. This system was built with chemically inert materials. Air samples are grabbed quickly and alternately in two cylindrical reservoirs, whose internal pressures are regulated by a moving piston. It was designed to be operated either on ground or aboard an airplane (the French ATR-42 research aircraft). It is also compatible with most analysers since it transfers the air samples at a regulated pressure. For validating the system, DEC and EC measurements of CO 2 and latent heat fluxes were performed concurrently during a field campaign. EC fluxes were first compared to simulated DEC (SDEC) fluxes and then to actual DEC fluxes. The EC fluxes were in agreement with both the simulated and actual DEC fluxes. The EC fluxes compare well to SDEC fluxes ( R 2 = 0.92 and 0.68 for latent heat and CO 2 fluxes, respectively) and to actual DEC fluxes ( R 2 = 0.91 and 0.67 for latent heat and CO 2 fluxes, respectively), in spite of low fluxes experienced during the campaign. This good agreement between the two techniques demonstrates that MEDEE is suitable for DEC measurements and highlights the DEC method as a reliable alternative to EC for slower sensors. A first field campaign focused on biogenic volatile organic compound (BVOC) emissions was done to measure isoprene fluxes above a downy oak ( Quercus Pubescens ) forest in the southeast of France. The measured emission rates were in good agreement with the values reported in earlier studies. Further analysis will be conducted from ground-based and airborne campaigns in the forthcoming years.

Beschreibung: Comparison of N 2 O 5 mixing ratios during NO3Comp 2007 in SAPHIR Atmospheric Measurement Techniques Discussions, 5, 4927-4967, 2012 Author(s): H. Fuchs, W. R. Simpson, R. L. Apodaca, T. Brauers, R. C. Cohen, J. N. Crowley, H.-P. Dorn, W. P. Dubé, J. L. Fry, R. Häseler, Y. Kajii, A. Kiendler-Scharr, I. Labazan, J. Matsumoto, T. F. Mentel, Y. Nakashima, F. Rohrer, A. W. Rollins, G. Schuster, R. Tillmann, A. Wahner, P. J. Wooldridge, and S. S. Brown N 2 O 5 detection in the atmosphere has been accomplished using techniques which have been developed during the last decade. Most techniques use a heated inlet to thermally decompose N 2 O 5 to NO 3 , which can be detected by either cavity based absorption at 662 nm or by laser-induced fluorescence. In summer 2007, a large set of instruments, which were capable of measuring NO 3 mixing ratios, were simultaneously deployed in the atmosphere simulation chamber SAPHIR in Jülich, Germany. Some of these instruments measured N 2 O 5 mixing ratios either simultaneously or alternatively. Experiments focussed on the investigation of potential interferences from e.g. water vapor or aerosol and on the investigation of the oxidation of biogenic volatile organic compounds by NO 3 . The comparison of N 2 O 5 mixing ratios shows an excellent agreement between measurements of instruments applying different techniques (3 cavity ring-down (CRDS) instruments, 2 laser-induced fluorescence (LIF) instruments). Data sets are highly correlated as indicated by the square of the linear correlation coefficients, R 2 , which values are larger than 0.96 for the entire data sets. N 2 O 5 mixing ratios well agree within the combined accuracy of measurements. Slopes of the linear regression range between 0.87 and 1.26 and intercepts are negligible. The most critical aspect of N 2 O 5 measurements by cavity ring-down instruments is the determination of the inlet and filter transmission efficiency. Measurements here show that the N 2 O 5 inlet transmission efficiency can decrease in the presence of high aerosol loads, and that frequent filter/inlet changing is necessary to quantitatively sample N 2 O 5 in some environments. The analysis of data also demonstrates that a general correction for degrading filter transmission is not applicable for all conditions encountered during this campaign. Besides the effect of a gradual degradation of the inlet transmission efficiency aerosol exposure, no other interference for N 2 O 5 measurements is found.

Beschreibung: Calibration of the SBUV version 8.6 ozone data product Atmospheric Measurement Techniques Discussions, 5, 5151-5203, 2012 Author(s): M. T. DeLand, S. L. Taylor, L. K. Huang, and B. L. Fisher This paper describes the calibration process for the Solar Backscatter Ultraviolet (SBUV) Version 8.6 (V8.6) ozone data product. Eight SBUV instruments have flown on NASA and NOAA satellites since 1970, and a continuous data record is available since November 1978. The accuracy of ozone trends determined from these data depends on the calibration and long-term characterization of each instrument. V8.6 calibration adjustments are determined at the radiance level, and do not rely on comparison of retrieved ozone products with other instruments. The primary SBUV instrument characterization is based on prelaunch laboratory tests and dedicated on-orbit calibration measurements. We supplement these results with "soft" calibration techniques using carefully chosen subsets of radiance data and information from the retrieval algorithm output to validate each instrument's calibration. The estimated long-term uncertainty in albedo is approximately ±0.8–1.2% (1σ) for most of the instruments. The overlap between these instruments and the Shuttle SBUV (SSBUV) data allows us to intercalibrate the SBUV instruments to produce a coherent V8.6 data set covering more than 32 yr. The estimated long-term uncertainty in albedo is less than 3% over this period.

Beschreibung: Evaluation of factors affecting accurate measurements of atmospheric CO 2 and CH 4 by wavelength-scanned cavity ring-down spectroscopy Atmospheric Measurement Techniques Discussions, 5, 5009-5041, 2012 Author(s): H. Nara, H. Tanimoto, Y. Tohjima, H. Mukai, Y. Nojiri, K. Katsumata, and C. Rella We examined potential interferences from water vapor and atmospheric background gases (N 2 , O 2 , and Ar), and biases by isotopologues of target species, on accurate measurement of atmospheric CO 2 and CH 4 by means of wavelength-scanned cavity ring-down spectroscopy (WS-CRDS). Variations in the composition of the background gas substantially impacted the CO 2 and CH 4 measurements: the measured amounts of CO 2 and CH 4 decreased with increasing N 2 mole fraction, but increased with increasing O 2 and Ar, suggesting that the pressure-broadening effects (PBEs) increased as Ar 〈 O 2 〈 N 2 . Using these experimental results, we inferred PBEs for the measurement of synthetic standard gases. The PBEs were negligible (up to 0.05 ppm for CO 2 and 0.01 ppb for CH 4 ) for gas standards balanced with purified air, although the PBEs were substantial (up to 0.87 ppm for CO 2 and 1.4 ppb for CH 4 ) for standards balanced with synthetic air. For isotopic biases on CO 2 measurements, we compared experimental results and theoretical calculations, which showed excellent agreement within their uncertainty. We derived empirical correction functions for water vapor for three WS-CRDS instruments (Picarro EnviroSense 3000i, G-1301, and G-2301). Although the transferability of the functions was not clear, no significant difference was found in the water vapor correction values among these instruments within the typical analytical precision at sufficiently low water concentrations ( 〈 0.3%V for CO 2 and 〈 0.4%V for CH 4 ). For accurate measurements of CO 2 and CH 4 in ambient air, we concluded that WS-CRDS measurements should be performed under complete dehumidification of air samples, or moderate dehumidification followed by application of a water vapor correction function, along with calibration by natural air-based standard gases or purified air-balanced synthetic standard gases with isotopic correction.

Beschreibung: A fast method for the retrieval of integrated longwave and shortwave top-of-atmosphere irradiances from MSG/SEVIRI (RRUMS) Atmospheric Measurement Techniques Discussions, 5, 4969-5008, 2012 Author(s): M. Vázquez-Navarro, B. Mayer, and H. Mannstein A new R apid R etrieval of u pwelling fluxes from M SG/ S EVIRI (RRUMS) is presented. It has been developed to observe the top-of-atmosphere irradiances of small scale and rapidly changing features that are not sufficiently resolved by specific Earth radiation budget sensors. Our retrieval takes advantage of the spatial and temporal resolution of MSG/SEVIRI and provides outgoing longwave and reflected shortwave radiation only by means of a combination of SEVIRI channels. The longwave retrieval is based on a simple linear combination of brightness temperatures from the SEVIRI infrared channels. Two shortwave retrievals are presented and discussed: the first one based on a multilinear parameterisation and the second one based on a neural network. The neural network method is shown to be slightly more accurate and simpler to apply for the desired purpose. Both LW and SW algorithms have been validated by comparing their results with CERES and GERB irradiance observations. While being less accurate than their dedicated counterparts, the SEVIRI-based methods have two major advantages compared to CERES and GERB: their higher spatial resolution and the better temporal resolution. With our retrievals it is possible to observe the radiative effect of small-scale features such as cumulus clouds, cirrus clouds, or aircraft contrails. The spatial resolution of SEVIRI is 3 km × 3 km in the sub-satellite point, remarkably better than that of CERES (20 km) or GERB (45 km). The temporal resolution is 15 min (5 min in the rapid-scan mode), the same as GERB, but significantly better than that of CERES which, being on board of a polar orbiting satellite, has a temporal resolution as low as 2 overpasses per day.

Beschreibung: Retrieval of tropospheric NO 2 columns from SCIAMACHY combining measurements from limb and nadir geometries Atmospheric Measurement Techniques Discussions, 5, 5043-5105, 2012 Author(s): A. Hilboll, A. Richter, A. Rozanov, Ø. Hodnebrog, A. Heckel, S. Solberg, F. Stordal, and J. P. Burrows Satellite measurements of atmospheric trace gases have proved to be an invaluable tool for monitoring the Earth system. When these measurements are to be used for assessing tropospheric emissions and pollution, as for example in the case of nadir measurements of nitrogen dioxide (NO 2 ), it is necessary to separate the stratospheric from the tropospheric signal. The SCIAMACHY instrument offers the unique opportunity to combine its measurements in limb and nadir viewing geometries into a tropospheric data product, using the limb measurements of the stratospheric NO 2 abundances to correct the nadir measurements' total columns. In this manuscript, we present a novel approach to limb/nadir matching, calculating one stratospheric NO 2 value from limb measurements for every single nadir measurement, abandoning global coverage for the sake of spatial accuracy. As a comparison, modelled stratospheric NO 2 columns from the Oslo CTM2 are evaluated as stratospheric correction, and both datasets are confronted with the originally used reference sector method. Our study shows that stratospheric NO 2 columns from SCIAMACHY limb measurements very well reflect stratospheric conditions. The zonal variability of stratospheric NO 2 is captured by our matching algorithm, and the quality of the resulting tropospheric NO 2 columns improves considerably. Modelled stratospheric NO 2 columns from the Oslo CTM2 agree remarkably well with the measurements. Both datasets need to be matched to the level of the nadir measurements, however, because a time and latitude dependent bias between both stratospheric datasets and the measured nadir columns can be observed over clean regions. After accounting for this systematic bias between SCIAMACHY nadir observations and the stratospheric columns, both new stratospheric correction methods provide a significant improvement to the retrieval of tropospheric NO 2 columns from the SCIAMACHY instrument.

Beschreibung: Accuracy assessment of Aqua-MODIS aerosol optical depth over coastal regions: importance of quality flag and sea surface wind speed Atmospheric Measurement Techniques Discussions, 5, 5205-5243, 2012 Author(s): J. C. Anderson, J. Wang, J. Zeng, M. Petrenko, G. G. Leptoukh, and C. Ichoku Coastal regions around the globe are a major source for anthropogenic aerosols in the atmosphere, but the underlying surface characteristics are not favorable for the Moderate Resolution Imaging Spectroradiometer (MODIS) algorithms designed for retrieval of aerosols over dark land or open-ocean surfaces. Using data collected from 62 coastal stations worldwide from the Aerosol Robotic Network (AERONET) from ~ 2002–2010, accuracy assessments are made for coastal aerosol optical depth (AOD) retrieved from MODIS aboard Aqua satellite. It is found that coastal AODs (at 550 nm) characterized respectively by the MODIS Dark Land (hereafter Land) surface algorithm, the Open-Ocean (hereafter Ocean) algorithm, and AERONET all exhibit a log-normal distribution. After filtering by quality flags, the MODIS AODs respectively retrieved from the Land and Ocean algorithms are highly correlated with AERONET (with R 2 ≈ 0.8), but only the Land algorithm AODs fall within the expected error envelope greater than 66% of the time. Furthermore, the MODIS AODs from the Land algorithm, Ocean algorithm, and combined Land_and_Ocean product show statistically significant discrepancies from their respective counterparts from AERONET in terms of mean, probability density function, and cumulative density function, which suggest a need for future improvement in retrieval algorithms. Without filtering with quality flag, the MODIS Land_and_Ocean AOD dataset can be degraded by 30–50% in terms of mean bias. Overall, the MODIS Ocean algorithm overestimates the AERONET coastal AOD by 0.021 for AOD 〈 0.25 and underestimates it by 0.029 for AOD 〉 0.25. This dichotomy is shown to be related to the ocean surface wind speed and cloud contamination effects on the satellite aerosol retrieval. The Modern Era Retrospective-Analysis for Research and Applications (MERRA) reveals that wind speeds over the global coastal region (with a mean and median value of 2.94 m s −1 and 2.66 m s −1 , respectively) are often slower than 6 m s −1 assumed in the MODIS Ocean algorithm. As a result of high correlation ( R 2 〉 0.98) between the bias in binned MODIS AOD and the corresponding binned wind speed over the coastal sea surface, an empirical scheme for correcting the bias of AOD retrieved from the MODIS Ocean algorithm is formulated and is shown to be effective over the majority of the coastal AERONET stations, and hence can be used in future analysis of AOD trend and MODIS AOD data assimilation.

Beschreibung: Esrange lidar's new pure rotational-Raman channel for measurement of temperature and aerosol extinction in the troposphere and lower stratosphere Atmospheric Measurement Techniques Discussions, 5, 6455-6478, 2012 Author(s): P. Achtert, M. Khaplanov, F. Khosrawi, and J. Gumbel The Department of Meteorology at Stockholm University operates the Esrange Rayleigh/Raman lidar at Esrange (68° N, 21° E) near the Swedish city of Kiruna. This paper describes the design and first measurements of the new pure rotational-Raman channel of the Esrange lidar. The Esrange lidar uses a pulsed Nd:YAG solid-state laser operating at 532 nm as light source with a repetition rate of 20 Hz and a pulse energy of 350 mJ. The minimum vertical resolution 150 m and the integration time for one profile is 5000 shots. The newly implemented channel allows for measurements of atmospheric temperature at altitudes below 35 km and is currently optimized for temperature measurements between 180 and 200 K. This corresponds to conditions in the lower Arctic stratosphere during winter. In addition to the temperature measurements the aerosol extinction coefficient and the aerosol backscatter coefficient at 532 nm can be measured independently. Our filter-based design minimizes the systematic error in the obtained temperature profile to less than 0.51 K. By combining rotational-Raman measurements (5–35 km height) and the integration technique (30–80 km height), the Esrange lidar is now capable of measuring atmospheric temperature profiles from the lower troposphere up to the mesosphere. With the improved setup, the system can be used to validate current lidar-based polar stratospheric cloud classification schemes. The new capability of the instrument measuring temperature and aerosol extinction furthermore enables studies of the thermal structure and variability of the upper troposphere/lower stratosphere. Although several lidars are operated at polar latitudes, there are few instruments that are capable to measure temperature profiles in the troposphere, stratosphere, and mesosphere, as well as aerosols extinction in the troposphere and lower stratosphere with daylight capability.

Beschreibung: Cluster analysis of WIBS single particle bioaerosol data Atmospheric Measurement Techniques Discussions, 5, 6387-6422, 2012 Author(s): N. H. Robinson, J. D. Allan, J. A. Huffman, P. H. Kaye, V. E. Foot, and M. Gallagher Hierarchical agglomerative cluster analysis was performed on single-particle multi-spatial datasets comprising optical diameter, asymmetry and three different fluorescence measurements, gathered using two dual Waveband Integrated Bioaerosol Sensor (WIBS). The technique is demonstrated on measurements of various fluorescent and non-fluorescent polystyrene latex spheres (PSL) before being applied to two separate contemporaneous ambient WIBS datasets recorded in a forest site in Colorado, USA as part of the BEACHON-RoMBAS project. Cluster analysis results between both datasets are consistent. Clusters are tentatively interpreted by comparison of concentration time series and cluster average measurement values to the published literature (of which there is a paucity) to represent: non-fluorescent accumulation mode aerosol; bacterial agglomerates; and fungal spores. To our knowledge, this is the first time cluster analysis has been applied to long term online PBAP measurements. The novel application of this clustering technique provides a means for routinely reducing WIBS data to discrete concentration time series which are more easily interpretable, without the need for any a priori assumptions concerning the expected aerosol types. It can reduce the level of subjectivity compared to the more standard analysis approaches, which are typically performed by simple inspection of various ensemble data products. It also has the advantage of potentially resolving less populous or subtly different particle types. This technique is likely to become more robust in the future as fluorescence-based aerosol instrumentation measurement precision, dynamic range and the number of available metrics is improved.

Beschreibung: Position error in profiles retrieved from MIPAS observations with a 1-D algorithm Atmospheric Measurement Techniques Discussions, 5, 6519-6551, 2012 Author(s): M. Carlotti, E. Arnone, E. Castelli, B. M. Dinelli, and E. Papandrea The information load (IL) analysis, first introduced for the two-dimensional approach (Carlotti and Magnani, 2009), is applied to the inversion of MIPAS observations operated with a 1-dimensional (1-D) retrieval algorithm. The IL distribution of MIPAS spectra is shown to be often asymmetrical with respect to the tangent points of the observations and permits to identify the preferential latitude where the profiles retrieved with a 1-D algorithm should be geo-located. Therefore a position error is made when the tangent points of the observations are used to assign the geo-location of the retrieved profile. We assess the amplitude of the position error for some of the MIPAS main targets and we show that the IL analysis can also be used as a tool for the selection of observations that, when analyzed, minimize the position error of the retrieved profile. When the temperature ( T ) profiles are used for the retrieval of volume mixing ratio (VMR) of atmospheric constituents, the T position error (of the order of 1.5 degrees of latitude) induces a VMR error that is directly connected with the horizontal T gradients. Temperature profiles can be externally-provided or determined in a previous step of the retrieval process. In the first case, the IL analysis shows that a meaningful fraction (often exceeding 50%) of the VMR error deriving from the 1-D approximation is to be attributed to the mismatch between the position assigned to the external T profile and the positions where T is required by the analyzed observations. In the second case the retrieved T values suffer by an error of 1.5–2 K due to neglecting the horizontal variability of T ; however the error induced on VMRs is of minor entity because of the generally small mismatch between the IL distribution of the observations analyzed to retrieve T and those analyzed to retrieve the VMR target. An estimate of the contribution of the T -position error to the error budget is provided for MIPAS main targets. This study shows that the information load analysis can be successfully exploited in a 1-D context that makes the assumption of horizontal homogeneity of the analyzed portion of atmosphere. The analysis that we propose can be extended to the 1-D inversion of other limb-sounding experiments.

Beschreibung: The CM SAF SSM/I-based total column water vapour climate data record: methods and evaluation against re-analyses and satellite Atmospheric Measurement Techniques Discussions, 5, 6423-6453, 2012 Author(s): M. Schröder, M. Jonas, R. Lindau, J. Schulz, and K. Fennig The "European Organisation for the Exploitation of Meteorological Satellites" (EUMETSAT) Satellite Application Facility on Climate Monitoring (CM SAF) aims at the provision and sound validation of well documented Climate Data Records (CDRs) in sustained and operational environments. In this study, a total column water vapour (WVPA) climatology from CM SAF is presented and inter-compared to water vapour data records from various data sources. Based on homogenised brightness temperatures from the Special Sensor Microwave Imager (SSM/I), a climatology of WVPA has been generated within the Hamburg Ocean-Atmosphere Fluxes and Parameters from Satellite (HOAPS) framework. Within a research and operation transition activity the HOAPS data and operations capabilities have been successfully transferred to the CM SAF where the complete HOAPS data and processing schemes are hosted in an operational environment. An objective analysis for interpolation, kriging, has been developed and applied to the swath-based WVPA retrievals from the HOAPS data set. The resulting climatology consists of daily and monthly mean fields of WVPA over the global ice-free ocean. The temporal coverage ranges from July 1987 to August 2006. After a comparison to the precursor product the CM SAF SSM/I-based climatology has been comprehensively compared to different types of meteorological analyses from the European Centre for Medium-Range Weather Forecasts (ECMWF-ERA40, ERA INTERIM and operational analyses) and from the Japan Meteorological Agency (JMA-JRA). This inter-comparison shows an overall good agreement between the climatology and the analyses, with daily absolute biases generally smaller than 2 kg m −2 . The absolute bias to JRA and ERA INTERIM is typically smaller than 0.5 kg m −2 . For the period 1991–2006, the root mean square error (RMSE) to both reanalysis is approximately 2 kg m −2 . As SSM/I WVPA and radiances are assimilated in JMA and all ECMWF analyses and to assess consistency to existing WVPA climatologies, the SSM/I-based climatology is also compared to the time series of SSM/I WVPA from Remote Sensing Systems (RSS), leading to results consistent with the reanalyses results. This evaluation study gives confidence in consistency, accurateness and stability of the total water vapour climatology produced.

Beschreibung: Accurate measurements of carbon monoxide in humid air using the cavity ring-down spectroscopy (CRDS) technique Atmospheric Measurement Techniques Discussions, 5, 6493-6517, 2012 Author(s): H. Chen, A. Karion, C. W. Rella, J. Winderlich, C. Gerbig, A. Filges, T. Newberger, C. Sweeney, and P. P. Tans Accurate measurements of carbon monoxide (CO) in humid air have been made using the cavity ring-down spectroscopy (CRDS) technique. The measurements of CO mole fractions are determined from the strength of its spectral absorption in the near infrared region (∼1.57 μm) after removing interferences from adjacent carbon dioxide (CO 2 ) and water vapor (H 2 O) absorption lines. Water correction functions that account for the dilution and pressure-broadening effects as well as absorption line interferences from adjacent CO 2 and H 2 O lines have been derived for CO 2 mole fractions between 360–390 ppm. The line interference corrections are independent of CO mole fractions. The dependence of the line interference correction on CO 2 abundance is estimated to be approximately −0.3 ppb/100 ppm CO 2 for dry mole fractions of CO. Comparisons of water correction functions from different analyzers of the same type show significant differences, making it necessary to perform instrument-specific water tests for each individual analyzer. The CRDS analyzer was flown on an aircraft in Alaska from April to November in 2011, and the accuracy of the CO measurements by the CRDS analyzer has been validated against discrete NOAA/ESRL flask sample measurements made on board the same aircraft, with a mean difference between integrated in situ and flask measurements of −0.6 ppb and a standard deviation of 2.8 ppb. Preliminary testing of CRDS instrumentation that employs new spectroscopic analysis (available since the beginning of 2012) indicates a smaller water vapor dependence than the models discussed here, but more work is necessary to fully validate the performance. The CRDS technique provides an accurate and low-maintenance method of monitoring the atmospheric dry mole fractions of CO in humid air streams.

Beschreibung: Correction for a measurement artifact of the Multi-Angle Absorption Photometer (MAAP) at high black carbon mass concentration levels Atmospheric Measurement Techniques Discussions, 5, 6553-6576, 2012 Author(s): A.-P. Hyvärinen, V. Vakkari, L. Laakso, R. K. Hooda, V. P. Sharma, T. S. Panwar, J. P. Beukes, P. G. van Zyl, M. Josipovic, R. M. Garland, M. O. Andreae, U. Pöschl, and A. Petzold The Multi-Angle Absorption Photometer (MAAP) is a widely-used instrument for aerosol black carbon observations. In this paper, we show correction methods for an artifact found to affect the instrument accuracy in environments with high black carbon concentrations. The artifact occurs after a filter spot change – as BC mass is accumulated on a fresh filter spot, the attenuation of the light (raw signal) is weaker than anticipated. This causes a sudden decrease, followed by a gradual increase in measured BC concentration. The artifact is present in the data when the BC concentration exceeds ∼3 μg m −3 at the typical MAAP flow rate of 16.7 l min −1 or 1 m 3 h −1 . The artifact is caused by erroneous dark counts in the photo detector measuring the transmitted light, in combination with an instrument internal averaging procedure of the photo detector raw signals. It was found that in addition to the erroneous temporal response of the data, concentrations higher than 9 μg m −3 (at the flow rate of 16.7 l min −1 ) are underestimated by the MAAP. The underestimation increases with increasing BC accumulation rate. At a flow rate of 16.7 l min −1 and concentration of about 24 μg m −3 (BC accumulation rate ∼0.4 μg min −1 ), the underestimation is about 30%. There are two ways of overcoming the MAAP artifact. One method is by logging the raw signal of the 165° photomultiplier measuring the reflected light from the filter spot. As this signal is not affected by the artifact, it can be converted to approximately correct absorption and BC values. However, as the typical print formats of the MAAP do not give the reflected signal as an output, a semi-empirical correction method was developed based on laboratory experiments to correct for the results in the post-processing phase. The correction function was applied to three MAAP datasets from Gual Pahari (India), Beijing (China), and Welgegund (South Africa). In Beijing, the results could also be compared against a Photo-Acoustic Spectrometer (PAS). The correction improved the quality of all three MAAP datasets substantially, even though the individual instruments operated at different flow rates and in different environments.

Beschreibung: Jena Reference Air Set (JRAS): a multi-point scale anchor for isotope measurements of CO 2 in air Atmospheric Measurement Techniques Discussions, 5, 6627-6642, 2012 Author(s): M. Wendeberg, J. M. Richter, M. Rothe, and W. A. Brand The need for a unifying scale anchor for isotopes of CO 2 in air was brought to light at the WMO CO 2 Experts Meeting in Tokyo 2001. During discussions about persistent discrepancies in isotope measurements between the worlds leading laboratories it was concluded that a unifying scale anchor for VPDB of CO 2 in air was desperately needed. Now, 10 yr later, the 2011 CO 2 -Experts-Meeting in Wellington has decided that the Jena Reference Air Set or JRAS is recommended as official scale anchor for isotope measurements of CO 2 in air. The JRAS gases consist of reference CO 2 mixed into CO 2 free air. To safeguard both stability and longevity of the CO 2 , it is directly generated from two solid reference calcites. That the reference CO 2 is supplied in air is unique to JRAS. This is made to ensure that any measurement bias arising from the extraction procedure is eliminated. As every lab has its own procedure for extracting the CO 2 this is of paramount importance if the local scales are to be unified. For a period of four years, JRAS has been evaluated through the IMECC program, which made it possible to distribute sets of JRAS gases to 11 laboratories worldwide. A summary of the results is reported here along with a description of the production and maintenance of the JRAS scale anchors.

Beschreibung: Improving retrieval quality for airborne limb-sounders by horizontal regularisation Atmospheric Measurement Techniques Discussions, 5, 6577-6626, 2012 Author(s): J. Ungermann Modern airborne infrared limb-sounders are capable of measuring profiles so fast that neighbouring profiles are very similar to one another. This can be exploited by retrieving whole 2-D cross-sections instead of simple 1-D profiles. By adding horizontal regularisation in addition to a potentially reduced vertical regularisation, vertical structures can be better retrieved while maintaining or reducing the general noise level. This paper presents algorithms that are able to perform such a retrieval and efficiently produce typical diagnostic quantities. The characteristics of produced retrieval results for a variety of parametrisations is discussed in a case study that analyses a cross-section measured by the CRISTA-NF instrument during the RECONCILE campaign between Spitsbergen and Kiruna, Sweden, in March 2010. It is shown that cross-section retrievals can either reduce noise or produce finer vertical structures while maintaining the same noise level. The presented methodology can also be applied in a straightforward way to improve the retrievals for both near-future satellite-borne limb-sounders and current air- and satellite-borne nadir sounder.

Beschreibung: Improving Langley calibrations by reducing diurnal variations of aerosol Ångström parameters Atmospheric Measurement Techniques Discussions, 5, 6479-6492, 2012 Author(s): A. Kreuter, S. Wuttke, and M. Blumthaler Errors in the sun photometer calibration constant lead to artificial diurnal variations, symmetric around solar noon, of the retrieved Aerosol Optical Depth (AOD) and the associated Ångström exponent α and its curvature γ . We show in simulations that within the uncertainty of state-of-the-art Langley calibrations, these diurnal variations of α and γ can be significant in low AOD conditions, while those of AOD are negligible. We implement a weighted Monte-Carlo method of finding an improved calibration constant by minimizing the diurnal variations in α and γ and apply the method to sun photometer data of a clear day in Innsbruck, Austria. The results show that our method can be used to improve the calibrations in two of the four wavelength channels by up to a factor of 3.6.

Beschreibung: HDO/H 2 O ratio retrievals from GOSAT Atmospheric Measurement Techniques Discussions, 5, 6643-6677, 2012 Author(s): H. Boesch, N. M. Deutscher, T. Warneke, K. Byckling, A. J. Cogan, D. W. T. Griffith, J. Notholt, R. J. Parker, and Z. Wang We report a new shortwave infrared (SWIR) retrieval of the column-averaged HDO/H 2 O ratio from the Japanese Greenhouse Gases Observing SATellite (GOSAT). From synthetic simulation studies, we have estimated that the inferred δ D values will typically have random errors between 20‰ (desert surface and 30° solar zenith angle) and 120‰ (conifer surface and 60° solar zenith angle). We find that the retrieval will have a small, but significant sensitivity to the presence of cirrus clouds, the HDO a priori profile shape and atmospheric temperature, which has the potential for introducing some regional-scale biases in the retrieval. From comparisons to ground-based column observations from the Total Carbon Column Observing Network (TCCON) we find differences between δ D from GOSAT and TCCON of around −30‰ for northern-hemispheric sites which increase up to −70‰ for Australian sites. The bias for the Australian sites significantly reduces when decreasing the spatial co-location criteria, which shows that spatial averaging contributes to the observed differences over Australia. The GOSAT retrievals allow mapping the global distribution of δ D and its variations with season and we find in our global GOSAT retrievals the expected strong latitudinal gradients with significant enhancements over the tropics. The comparisons to the ground-based TCCON network and the results of the global retrieval are very encouraging and they show that δ D retrieved from GOSAT should be a useful product that can be used to complement datasets from thermal-infrared sounder and ground-based networks and to extend the δ D dataset from SWIR retrievals established from the recently ended SCIAMACHY mission.

Beschreibung: Quality assessment of Automatic Dependent Surveillance Contract (ADS-C) wind and temperature observation from commercial aircraft Atmospheric Measurement Techniques Discussions, 5, 5617-5639, 2012 Author(s): S. de Haan, L. J. Bailey, and J. E. Können Aircraft observations of wind and temperature are very important for upper air meteorology. In this article, the quality of the meteorological information of an Automatic Dependent Surveillance-Contract (ADS-C) message is assessed. The ADS-C messages are received at air traffic control centres for surveillance and airline control centres for general aircraft and dispatch management. Comparison against a global numerical prediction (NWP) model and Mode-S Enhanced Surveillance (EHS) derived wind and temperature observations is performed. Almost 16 thousand ADS-C reports with meteorological information were compiled from the Royal Dutch Airlines (KLM) database. The length of the data set is 76 days. The wind and temperature observations are of good quality when compared to the global NWP forecast fields from the European Centre for Medium-Range Weather Forecasts (ECMWF). Comparison of ADS-C wind and temperature observations against Mode-S EHS derived observations in the vicinity of Amsterdam Airport Schiphol shows that the wind observations are of similar quality and the temperature observations of ADS-C are of better quality than those from Mode-S EHS. However, the current ADS-C data set has a lower vertical resolution than Mode-S EHS. High vertical resolution can be achieved by requesting more ADS-C when aircraft are ascending or descending, but could result in increased data communication costs.

Beschreibung: A comparison of in-situ aircraft measurements of carbon dioxide to GOSAT data measured over Railroad Valley playa, Nevada, USA Atmospheric Measurement Techniques Discussions, 5, 5641-5664, 2012 Author(s): J. M. Tadić, M. Loewenstein, C. Frankenberg, L. T. Iraci, E. L. Yates, W. Gore, and A. Kuze In this paper we report vertical profiles of CO 2 measured with a cavity ring-down spectrometer (CRDS, Picarro, Inc., 2301-m) on a research aircraft from near ground level to 8 km above mean sea level (a.m.s.l.). The airborne platform employed in this study is an Alpha Jet aircraft operated from NASA Ames Research Center. Flights were undertaken to Railroad Valley, Nevada, USA, to coincide with overpasses of the Greenhouse Gases Observing Satellite (GOSAT). Ground based CO 2 was simultaneously measured using CRDS, also at the time and location of the airborne and satellite measurements. Results of three GOSAT coordinated aircraft profiles and ground based measurements in June 2011 are presented and discussed in this paper. The accuracy of the CO 2 measurements has been determined based upon laboratory calibrations (WMO traceable standard) and pressure/temperature flight simulations in a test chamber. The 2-σ error bars for the CO 2 data presented here are ± 0.4 ppm. Our column CO 2 measurements, which include about 85% of the tropospheric mass, are extrapolated, using two different techniques, to include the remainder of the tropospheric and stratospheric CO 2 . The data are then analyzed using the ACOS (Atmospheric CO 2 observations from space; JPL algorithm used to analyze XCO 2 from GOSAT data) averaging kernels. ACOS version 2.9 is used to interpret the GOSAT data in a collaborative effort between JPL and the GOSAT team. Column averaged CO 2 , XCO 2 , measured by GOSAT and analyzed from our data ranged from 388.1 to 390.5 ppm. Values of XCO 2 determined from our Alpha Jet measurements and from the GOSAT on three overflight days agree within 1 ppm or better (

Beschreibung: Novel method for fog monitoring using cellular networks infrastructures Atmospheric Measurement Techniques Discussions, 5, 5725-5752, 2012 Author(s): N. David, P. Alpert, and H. Messer A major detrimental effect of fog is visibility limitation which can result in serious transportation accidents, traffic delays and therefore economic damage. Existing monitoring techniques including satellites, transmissometers and human observers – suffer from low spatial resolution, high cost or lack of precision when measuring near ground level. Here we show a novel technique for fog monitoring using wireless communication systems. Communication networks widely deploy commercial microwave links across the terrain at ground level. Operating at frequencies of tens of GHz they are affected by fog and are, effectively, an existing, spatially world-wide distributed sensor network that can provide crucial information about fog concentration and visibility. Fog monitoring potential is demonstrated for a heavy fog event that took place in Israel. The correlation between transmissomters and human eye observations to the visibility estimates from the nearby microwave links was found to be 0.53 and 0.61, respectively. These values indicate the high potential of the proposed method.

Beschreibung: Calibration and validation of water vapour lidar measurements from Eureka, Nunavut using radiosondes and the Atmospheric Chemistry Experiment fourier transform spectrometer Atmospheric Measurement Techniques Discussions, 5, 5665-5689, 2012 Author(s): A. Moss, R. J. Sica, E. McCullough, K. Strawbridge, K. Walker, and J. Drummond The Canadian Network for the Detection of Atmospheric Change and Environment Canada DIAL lidar located at the Polar Environment Atmospheric Research Laboratory (PEARL) in Eureka, Nunavut has been upgraded to measure water vapour mixing ratio profiles at 150 m vertical resolution. The system is capable of measuring water vapour in the dry arctic atmosphere up to the tropopause region. Measurements were obtained in the February to March polar sunrise during 2007, 2008 and 2009 as part of the Canadian Arctic ACE Validation Campaign. Before such measurements can be used to address important questions in understanding dynamics and chemistry, the lidar measurements must be calibrated against an independent determination of water vapour. Here, radiosonde measurements of relative humidity have been used to calibrate the lidar measurements. It was found that the calibration varied significantly between each campaign. However, the calibration of the lidar during an individual polar sunrise campaign agrees with the local radiosonde measurements to better than 12% below 6 km altitude. To independently validate the calibration of the lidar derived from the radiosondes, comparisons are made between the calibrated lidar measurements and water vapour measurements from the Atmospheric Chemistry Experiment satellite-borne Fourier Transform Spectrometer. The comparisons between the lidar and satellite for both campaign averages and single overpasses show favourable agreement between the two instruments and help validate the comparison with the radiosondes.

Beschreibung: XCO 2 -measurements with a tabletop FTS using solar absorption spectroscopy Atmospheric Measurement Techniques Discussions, 5, 5691-5724, 2012 Author(s): M. Gisi, F. Hase, S. Dohe, T. Blumenstock, A. Simon, and A. Keens A commercial low-resolution (0.5 cm −1 ) Fourier-Transform-Spectrometer (FTS) has been modified and is used for determining the total column XCO 2 of the atmosphere by analyzing direct solar radiation. The spectrometer has a small home-built solar tracker attached, so that it is a ready-to-use instrument. The results are validated with temporally coinciding on-site measurements taken with a high-resolution Total Carbon Column Observing Network (TCCON) FTIR-spectrometer. For the whole comparison period of 5 months (26 measurement days) an agreement with TCCON-results of (0.12 ± 0.08)% is achieved. This makes the spectrometer a promising candidate for a low-cost addition to the TCCON core FTIR sites, especially suitable for locations with limited infrastructure. An impressive mechanical and thermal stability is proved, enabling the spectrometer for use in field campaigns and for the monitoring of local sources.

Beschreibung: Usability of optical spectrum analyzer in measuring atmospheric CO 2 and CH 4 column densities: substantiation with FTS and aircraft profiles in situ Atmospheric Measurement Techniques Discussions, 5, 4099-4121, 2012 Author(s): M. Kawasaki, H. Yoshioka, N. B. Jones, R. Macatangay, D. W. T. Griffith, S. Kawakami, H. Ohyama, T. Tanaka, I. Morino, O. Uchino, and T. Ibuki The practical usefulness of a desktop optical spectrum analyzer (OSA) for measuring atmospheric CO 2 and CH 4 column densities at surface sites was examined in two separate measurement campaigns. The first involved a long term measurement in parallel with a high resolution Fourier transform spectroscopy (FTS) studies at the University of Wollongong in Australia. Scale factors of the OSA were assigned for the column average volume mixing ratios of x CO 2 and x CH 4 by comparing with the well-studied FTS. The second method is a calibration against aircraft CO 2 profiles in situ over Tsukuba in Japan obtained during a GOSAT validation campaign carried out from 28 January to 7 February 2011. The x CO 2 values in the campaign, deduced by use of a derived OSA scale factor, were in excellent agreement with the integrated aircraft profiles.

Beschreibung: Retrieval interval mapping, a tool to optimize the spectral retrieval range in differential optical absorption spectroscopy Atmospheric Measurement Techniques Discussions, 5, 4195-4247, 2012 Author(s): L. Vogel, H. Sihler, J. Lampel, T. Wagner, and U. Platt Remote sensing via differential optical absorption spectroscopy (DOAS) has become a standard technique to identify and quantify trace gases in the atmosphere. The technique is applied in a variety of configurations, commonly classified into active and passive instruments using artificial and natural light sources, respectively. Platforms range from ground based to satellite instruments and trace-gases are studied in all kinds of different environments. Due to the wide range of measurement conditions, atmospheric compositions and instruments used, a specific challenge of a DOAS retrieval is to optimize the parameters for each specific case and particular trace gas of interest. This becomes especially important when measuring close to the detection limit. A well chosen evaluation wavelength range is crucial to the DOAS technique. It should encompass strong absorption bands of the trace gas of interest in order to maximize the sensitivity of the retrieval, while at the same time minimizing absorption structures of other trace gases and thus potential interferences. Also, instrumental limitations and wavelength depending sources of errors (e.g. insufficient corrections for the Ring effect and cross correlations between trace gas cross sections) need to be taken into account. Most often, not all of these requirements can be fulfilled simultaneously and a compromise needs to be found depending on the conditions at hand. Although for many trace gases the overall dependence of common DOAS retrieval on the evaluation wavelength interval is known, a systematic approach to find the optimal retrieval wavelength range and qualitative assessment is missing. Here we present a novel tool to determine the optimal evaluation wavelength range. It is based on mapping retrieved values in the retrieval wavelength space and thus visualize the consequence of different choices of retrieval spectral ranges, e.g. caused by slightly erroneous absorption cross sections, cross correlations and instrumental features. The technique is demonstrated using the examples of a theoretical study of BrO retrievals for stratospheric BrO measurements and for BrO measurements in volcanic plumes. However, due to the general nature of the tool, it is applicable to any type (active or passive) of DOAS retrieval.

Beschreibung: Observation of volcanic ash from Puyehue-Cordón Caulle with IASI Atmospheric Measurement Techniques Discussions, 5, 4249-4283, 2012 Author(s): L. Klüser, T. Erbertseder, and J. Meyer-Arnek On 4 June 2011 an eruption of the Chilean volcano complex Puyehue-Cordón Caulle injected large amounts of volcanic ash into the atmosphere and affected local life as well as hemisphere-wide air traffic. Observations of the Infrared Atmospheric Sounding Interferometer IASI flown on board of the MetOp satellite have been exploited to analyze the evolution of the ash plume around the Southern Hemisphere. A novel Singular Vector based retrieval methodology, originally developed for observation of desert dust over land and ocean, has been adapted to enable remote sensing of volcanic ash. Since IASI observations in the 8–12 μm window are applied in the retrieval, the method is insensitive to solar illumination and therefore yields twice the observation rate of the ash plume evolution compared to solar backscatter methods from polar orbiting satellites. The retrieval scheme, the emission characteristics and the circumpolar transport of the ash are examined by means of a source-receptor analysis.

Beschreibung: Evaluation of three new laser spectrometer techniques for in-situ carbon monoxide measurements Atmospheric Measurement Techniques Discussions, 5, 4735-4769, 2012 Author(s): C. Zellweger, M. Steinbacher, and B. Buchmann Long-term time series of the atmospheric composition are essential for environmental research and thus require compatible, multi-decadal monitoring activities. However, the current data quality objectives of the World Meteorological Organization (WMO) for carbon monoxide (CO) in the atmosphere are very challenging to meet with the measurement techniques that have been used until recently. During the past few years, new spectroscopic techniques came on the market with promising properties for trace gas analytics. The current study compares three instruments that are recently commercially available (since 2011) with the up to now best available technique (vacuum UV fluorescence) and provides a link to previous comparison studies. The instruments were investigated for their performance regarding repeatability, reproducibility, drift, temperature dependence, water vapour interference and linearity. Finally, all instruments were examined during a short measurement campaign to assess their applicability for long-term field measurements. It could be shown that the new techniques provide a considerably better performance compared to previous techniques, although some issues such as temperature influence and cross sensitivities need further attention.

Beschreibung: Volcanic SO 2 and SiF 4 visualization using 2-D thermal emission spectroscopy – Part 2: Wind propagation and emission fluxes Atmospheric Measurement Techniques Discussions, 5, 4599-4633, 2012 Author(s): A. Krueger, W. Stremme, R. Harig, and M. Grutter The technique for measuring two-dimensional (2-D) plumes of volcanic gases with thermal emission spectroscopy was described in Part 1 by Stremme et al. (2012). In that paper the instrumental aspects as well as retrieval strategies for obtaining the slant column images of SO 2 and SiF 4 , as well as animations of particular events observed at the Popocatépetl volcano, were presented. This work focuses on the procedures for determining the propagation speed of the gases and estimating an emission flux from the given image sequences. A 2-D column density distribution of a volcanic gas, available as time-consecutive frames, provides information of a wind-field and the average velocity at which the volcanic plume is propagating. The presented reconstruction method solves the equation of continuity as an ill-posed problem using mainly a Tikhonov-like regularization. It is observed from the available data sets that if the main direction of propagation is perpendicular to the line-of-sight, the algorithm works well for SO 2 which has the strongest signals, and also for SiF 4 in some favourable cases. Due to the similarity of the algorithm used here with the reconstruction methods used for profile retrievals based on optimal estimation theory, diagnostic tools like the averaging kernels can be calculated analogously and the information can be quantified as degrees of freedom. Thus, it is shown that the combination of wind-field and column distribution of the gas plume can provide the emission flux of the volcano both during day and night.

Beschreibung: Strato-mesospheric ClO observations by SMILES: error analysis and diurnal variation Atmospheric Measurement Techniques Discussions, 5, 4667-4710, 2012 Author(s): T. O. Sato, H. Sagawa, D. Kreyling, T. Manabe, S. Ochiai, K. Kikuchi, P. Baron, J. Mendrok, J. Urban, D. Murtagh, M. Yasui, and Y. Kasai Chlorine monoxide (ClO) is the key species for anthropogenic ozone loss in the middle atmosphere. We observed the ClO diurnal variation using the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) on the International Space Station which has a non sun-synchronous orbit. This is the first global observation of the ClO diurnal variation from the stratosphere up to the mesosphere. The SMILES observation reproduced the diurnal variation of stratospheric ClO, an enhancement during a daytime, as observed by the Microwave Limb Sounder on the Upper Atmosphere Research Satellite (UARS/MLS). Mesospheric ClO has shown a different diurnal behavior with an enhancement during nighttime. The ClO enhancement was found at a pressure of 0.02 hPa (about 70 km) with an amplitude of about 100 pptv and reached up to 0.01 hPa (80 km) in the zonal mean of 50° N–65° N in January–February 2010. The observation of mesospheric ClO was possible due to the 10–20 times better signal-to-noise ratio of the spectra than those of past microwave/submillimeter-wave limb-emission sounders. We performed a quantitative error analysis for the strato- and mesospheric ClO of the Level-2 research (L2r) product version 2.1.5 taking into account all possible error contributions; i.e. errors due to spectrum noise, smoothing and uncertainties in the radiative transfer model and instrument function. The SMILES L2r v2.1.5 ClO data are useful over the range 0.01 and 100 hPa with a total error of 10–30 pptv (about 10%) with averaging of 100 profiles. The vertical resolution is 3–5 km and 5–8 km for the stratosphere and mesosphere, respectively. The performance of the SMILES observation opens the new opportunity to investigate ClO up to the mesopause.

Beschreibung: Calibration and intercomparison of acetic acid measurements using proton transfer reaction mass spectrometry (PTR-MS) Atmospheric Measurement Techniques Discussions, 5, 4635-4665, 2012 Author(s): K. B. Haase, W. C. Keene, A. A. P. Pszenny, H. R. Mayne, R. W. Talbot, and B. C. Sive Acetic acid is one of the most abundant organic acids in the ambient atmosphere, with maximum mixing ratios reaching into the tens of parts per billion by volume (ppbv) range. The identities and associated magnitudes of the major sources and sinks for acetic acid are poorly characterized, due in part to the limitation in available measurement techniques. This paper demonstrates that Proton Transfer Reaction Mass Spectrometry (PTR-MS) can reliably quantify acetic acid vapor in ambient air. Three different PTR-MS configurations were calibrated at low ppbv mixing ratios using permeation tubes, which yielded calibration factors between 7.0 and 10.9 normalized counts per second per ppbv (ncps ppbv −1 ) at a drift tube field strength of 132 townsend (Td). Detection limits ranged from 0.06 to 0.32 ppbv with dwell times of 5 s. These calibration factors showed negligible humidity dependence. Using the experimentally determined calibration factors, PTR-MS measurements of acetic acid during the International Consortium for Atmospheric Research on Transport and Transformation (ICARTT) campaign were validated against results obtained using Mist Chambers coupled with Ion Chromatography (MC/IC). An orthogonal least squares linear regression of paired data yielded a slope of 1.14 ± 0.06 (2σ), an intercept of 0.049 ± 20 (2σ) ppbv, and an R 2 of 0.78. The median mixing ratio of acetic acid on Appledore Island, ME during the ICARTT campaign was 0.530 ± 0.025 ppbv with a minimum of 0.075 ± 0.004 ppbv, and a maximum of 3.555 ± 0.171 ppbv.

Beschreibung: On-orbit radiometric calibration of SWIR bands of TANSO-FTS onboard GOSAT Atmospheric Measurement Techniques Discussions, 5, 4711-4734, 2012 Author(s): Y. Yoshida, N. Kikuchi, and T. Yokota The Greenhouse gases Observing SATellite (GOSAT) was launched on 23 January 2009 to monitor global distributions of carbon dioxide and methane. The Thermal And Near-infrared Sensor for carbon Observation-Fourier Transform Spectrometer (TANSO-FTS) onboard GOSAT measures short-wavelength infrared (SWIR) spectrum, and its radiometric accuracy directly influences the accuracy of the retrieved greenhouse gas concentrations. From a 2.5-yr retrieval analysis of GOSAT data, we found that the minimum of the mean-squared value of the residuals (the difference between observed and fitted spectra) and the radiance adjustment factor (one of the ancillary parameter to be retrieved with the gas concentrations for adjusting the radiance level between the bands) changed with time, possibly due to inaccurate degradation correction. In this study, the radiometric degradation of TANSO-FTS was evaluated from the on-orbit solar calibration data and modeled as a function of time and wavenumber for each spectral band. The radiometric degradation of TANSO-FTS Band 1 (centered at 0.76 μm) after the launch was evaluated to be about 4 to 6%, varying with wavenumber, whereas the other two bands (Band 2: 1.6 μm and Band 3: 2.0 μm) showed about 1% degradation and small wavenumber dependency. When we applied the new degradation model in the retrieval analysis, the above-mentioned issues disappeared.

Beschreibung: Improved Micro Rain Radar snow measurements using Doppler spectra post-processing Atmospheric Measurement Techniques Discussions, 5, 4771-4808, 2012 Author(s): M. Maahn and P. Kollias The Micro Rain Radar (MRR) is a compact Frequency Modulated Continuous Wave (FMCW) system that operates at 24 GHz. The MRR is a low-cost, portable radar system that requires minimum supervision in the field. As such, the MRR is a frequently used radar system for conducting precipitation research. Current MRR drawbacks are the lack of a sophisticated post-processing algorithm to improve its sensitivity (currently at +3 dBz), spurious artefacts concerning radar receiver noise and the lack of high quality Doppler radar moments. Here we propose an improved processing method which is especially suited for snow observations and provides reliable values of effective reflectivity, Doppler velocity and spectral width. The proposed method is freely available on the web and features a noise removal based on recognition of the most significant peak. A dynamic dealiasing routine allows observations even if the Nyquist velocity range is exceeded. Collocated observations at 115 days of a MRR and a pulsed 35.2 GHz MIRA35 cloud radar show a very high agreement for the proposed method for snow, if reflectivities are larger than −5 dBz. The overall sensitivity is increased to −14 and −8 dBz, depending on range. The proposed method exploits the full potential of MRR's hardware and substantially enhances the use of Micro Rain Radar for studies of solid precipitation.

Beschreibung: Remote sensing of ice crystal asymmetry parameter using multi-directional polarization measurements – Part 1: Methodology and evaluation with simulated measurements Atmospheric Measurement Techniques Discussions, 5, 4321-4359, 2012 Author(s): B. van Diedenhoven, B. Cairns, I. V. Geogdzhayev, A. M. Fridlind, A. S. Ackerman, P. Yang, and B. A. Baum We present a new remote sensing technique to infer the average asymmetry parameter of ice crystals near cloud top from multi-directional polarization measurements. The method is based on previous findings that (a) complex aggregates of hexagonal crystals generally have scattering phase matrices resembling those of their components and (b) scattering phase matrices systematically vary with aspect ratios of crystals and their degree of microscale surface roughness. Ice cloud asymmetry parameters are inferred from multi-directional polarized reflectance measurements by searching for the closest fit in a look-up table of simulated polarized reflectances computed for cloud layers that contain individual hexagonal columns and plates with varying aspect ratios and roughness values. The asymmetry parameter of the hexagonal particle that leads to the best fit with the measurements is considered the retrieved value. For clouds with optical thickness less than 5, the cloud optical thickness must be retrieved simultaneously with the asymmetry parameter, while for optically thicker clouds the asymmetry parameter retrieval is independent of cloud optical thickness. Evaluation of the technique using simulated measurements based on the optical properties of a number of complex particles and their mixtures shows that the ice crystal asymmetry parameters are generally retrieved to within 5%, or about 0.04 in absolute terms. The retrieval scheme is largely independent of calibration errors, range and sampling density of scattering angles and random noise in the measurements. The approach can be readily applied to measurements of past, current and future airborne and satellite instruments that measure multi-directional polarized reflectances of ice-topped clouds.

Beschreibung: Development of a new data-processing method for SKYNET sky radiometer observations Atmospheric Measurement Techniques Discussions, 5, 4361-4407, 2012 Author(s): M. Hashimoto, T. Nakajima, O. Dubovik, M. Campanelli, H. Che, P. Khatri, T. Takamura, and G. Pandithurai In order to reduce uncertainty in the estimation of aerosol direct radiative forcing (DARF), it is important to improve the estimation of the single scattering albedo (SSA). In this study, we propose a new data-processing method to improve SSA retrievals for the SKYNET sky radiometer network, which is one of the growing number of networks of sun-sky photometers, such as NASA AERONET and others. There are several reports that SSA values from SKYNET have a bias compared to those from AERONET, which is regarded to be the most accurate due to its rigorous calibration routines. We investigated possible causes of errors in SSA that might explain the known biases through sensitivity experiments using a numerical model, and also using real data at the SKYNET sites at Pune (18.616° N/73.800° E) in India and Beijing (39.586° N/116.229° E) in China. Sensitivity experiments showed that an uncertainty of the order of ±0.03 in the SSA value can be caused by a possible error in the ground surface albedo or solid view angle assumed for each observation site. Another candidate for possible error in the SSA was found in cirrus contamination generated by imperfect cloud screening in the SKYNET data processing. Therefore, we developed a new data quality control method that eliminates these error sources, and we applied this method to the real observation data at the Pune site in SKYNET. After applying this method to the observation data, we were able to screen out a large amount of cirrus-contaminated data and to reduce the deviation in the SSA value from that of AERONET. We then estimated DARF using data screened by our new method. The result showed that the method significantly reduced the difference of 5 W m −2 that existed between the SKYNET and AERONET values of DARF before screening. The present study also suggests the necessity of preparing suitable a priori information on the distribution of coarse particles ranging in radius between 10 μm and 30 μm for the analysis of heavily dust-laden atmospheric cases.

Beschreibung: SCIAMACHY WFM-DOAS XCO 2 : reduction of scattering related errors Atmospheric Measurement Techniques Discussions, 5, 4285-4320, 2012 Author(s): J. Heymann, H. Bovensmann, M. Buchwitz, J. P. Burrows, N. M. Deutscher, J. Notholt, M. Rettinger, M. Reuter, O. Schneising, R. Sussmann, and T. Warneke Global observations of column-averaged dry air mole fractions of carbon dioxide (CO 2 ), denoted by XCO 2 , retrieved from passive remote sensing instruments on Earth orbiting satellites can provide important and missing global information on the distribution and magnitude of regional CO 2 surface fluxes. This application has challenging precision and accuracy requirements. SCIAMACHY on-board ENVISAT is the first satellite instrument, which measures the upwelling electromagnetic radiation in the near and short wave infrared at an adequate spectral and spatial resolution to yield near-surface sensitive XCO 2 . In a previous publication (Heymann et al., 2012), it has been shown by analysing seven years of SCIAMACHY WFM-DOAS XCO 2 (WFMDv2.1) that unaccounted thin cirrus clouds can result in significant errors. In order to enhance the quality of the SCIAMACHY XCO 2 data product, we have developed a new version of the retrieval algorithm (WFMDv2.2), which is described in this manuscript. It is based on an improved cloud filtering and correction method using the 1.4 μm strong water vapour absorption and 0.76 μm O 2 -A bands. The new algorithm has been used to generate a SCIAMACHY XCO 2 data set covering the years 2003–2009. The new XCO 2 data set has been validated using ground-based observations from the Total Carbon Column Observing Network (TCCON). The validation shows a significant improvement of the new product (v2.2) in comparison to the previous product (v2.1). For example, the standard deviation of the difference to TCCON at Darwin, Australia, has been reduced from 4 ppm to 2 ppm. The monthly regional-scale scatter of the data (defined as the mean inner monthly standard deviation of all quality filtered XCO 2 retrievals within a radius of 350 km around various locations) has also been reduced, typically by a factor of about 1.5. Overall, the validation of the new WFMDv2.2 XCO 2 data product can be summarised by a single measurement precision of 3.8 ppm, an estimated regional-scale (radius of 500 km) precision of monthly averages of 1.6 ppm and an estimated regional-scale relative accuracy of 0.8 ppm. In addition to the comparison with the limited number of TCCON sites, we also present a comparison with NOAA's global CO 2 modelling and assimilation system CarbonTracker. This comparison also shows significant improvements especially over the Southern Hemisphere.

Beschreibung: 1 km fog and low stratus detection using pan-sharpened MSG SEVIRI data Atmospheric Measurement Techniques Discussions, 5, 4409-4446, 2012 Author(s): H. M. Schulz, B. Thies, J. Cermak, and J. Bendix In this paper a new technique for the detection of fog and low stratus in 1 km resolution from MSG SEVIRI data is presented. The method relies on the pan-sharpening of 3 km narrow-band channels using the 1 km high-resolution visible (HRV) channel. As solar and thermal channels had to be sharpened for the technique, a new approach based on an existing pan-sharpening method was developed using local regressions. A fog and low stratus detection scheme originally developed for 3 km SEVIRI data was used as the basis to derive 1 km resolution fog and low stratus masks from the sharpened channels. The sharpened channels and the fog and low stratus masks based on them were evaluated visually and by various statistical measures. The sharpened channels deviate only slightly from reference images regarding their pixel values as well as spatial features. The 1 km fog and low stratus masks are therefore deemed of high quality. They contain many details, especially where fog is restricted by complex terrain in its extent, that cannot be detected in the 3 km resolution.

Beschreibung: Profiling tropospheric CO 2 using the Aura TES and TCCON instruments Atmospheric Measurement Techniques Discussions, 5, 4495-4534, 2012 Author(s): L. Kuai, J. Worden, S. Kulawik, K. Bowman, S. Biraud, J. B. Abshire, S. C. Wofsy, V. Natraj, C. Frankenberg, D. Wunch, B. Connor, C. Miller, C. Roehl, R.-L. Shia, and Y. Yung Monitoring the global distribution and long-term variations of CO 2 sources and sinks is required for characterizing the global carbon budget. Although total column measurements will be useful for estimating large regional fluxes, model transport error remains a significant error source, particularly for local sources and sinks. To improve the capability of estimating regional fluxes, we estimate near-surface CO 2 values from ground-based near infrared (NIR) measurements with space-based thermal infrared (TIR) measurements. The NIR measurements are obtained from the Total Carbon Column Observing Network (TCCON) of solar measurements which provide an estimate of the total CO 2 atmospheric column amount. Estimates of tropospheric CO 2 that are co-located with TCCON are obtained by assimilating Tropospheric Emission Spectrometer (TES) free-tropospheric CO 2 estimates into the GEOS-Chem model. Estimates of the boundary layer CO 2 are obtained through simple subtraction, as the CO 2 estimation problem is linear. We find that the calculated random uncertainties in total column and boundary layer estimates are consistent with actual uncertainties as compared to aircraft data. For the total column estimates the random uncertainty is about 0.55 ppm with a bias of −5.66 ppm, consistent with previously published results. After accounting for the total column bias, the bias in the boundary layer CO 2 estimates is 0.26 ppm with a precision of 1.02 ppm This precision is sufficient for capturing the winter to summer variability of approximately 12 ppm in the lower troposphere; double the variability of the total column. This work shows that a combination of NIR and IR measurements can profile CO 2 with the precisions and accuracy needed to quantify near-surface CO 2 variability.

Beschreibung: Preliminary observation of temperature profiles by radio acoustic sounding system (RASS) with a 1280 MHz lower atmospheric wind profiler at Gadanki, India Atmospheric Measurement Techniques Discussions, 5, 4447-4472, 2012 Author(s): T. V. Chandrasekhar Sarma, P. Srinivasulu, and T. Tsuda A UHF wind profiler operating at 1280 MHz has been developed at NARL for atmospheric studies in the planetary boundary layer. In order to explore application of radio acoustic sounding system (RASS) technique to this profiler, a suitable acoustic attachment was designed and preliminary experiments were conducted on 27–30 August 2010. Height profiles of virtual temperature, T v , in the planetary boundary layer were derived with 1 μs and 0.25 μs pulse transmission, corresponding to a height resolution of 150 m and about 40 m, respectively. Diurnal variation of T v is clearly recognized, and perturbations of T v are also seen in association with a precipitation event. Simultaneous profiles obtained from the MST Radar-RASS and an onsite 50 m tower demonstrate the capability to continuously profile the atmospheric temperature from near the ground to upper tropospheric altitudes.

Beschreibung: An integrated flask sample collection system for greenhouse gas measurements Atmospheric Measurement Techniques Discussions, 5, 4077-4097, 2012 Author(s): J. Turnbull, D. Guenther, A. Karion, C. Sweeney, E. Anderson, A. Andrews, J. Kofler, N. Miles, T. Newberger, S. Richardson, and P. Tans A one hour integrated flask sampling system to collect air in automated NOAA/ESRL 12-flask packages is described. The integrating compressor system uses a mass flow controller to regulate the flow of air through a 15 l volume, thus providing a mixture of air collected over an hour-long period. By beginning with a high flow rate of 3800 standard liters per minute and gradually decreasing the flow rate over time to 290 standard liters per minute it is possible to obtain a nearly uniformly time averaged sample of air and collect it into a pressurized 0.7 l flask. The weighting function determining the air mixture obtained is described in detail. Laboratory and field tests demonstrate that the integrated sample approximates a simple mean of air collected during the one-hour sampling time.

Beschreibung: Six years of mesospheric CO estimated from ground-based frequency-switched microwave radiometry at 57° N compared with satellite instruments Atmospheric Measurement Techniques Discussions, 5, 3909-3952, 2012 Author(s): P. Forkman, O. M. Christensen, P. Eriksson, J. Urban, and B. Funke Measurements of mesospheric carbon monoxide, CO, provide important information about the dynamics in the mesosphere region since CO has a long lifetime at these altitudes. Ground-based measurements of mesospheric CO made at the Onsala Space Observatory, OSO, (57° N, 12° E) are presented. The dataset covers the period 2002–2008 and is hence uniquely long. The simple and stable 115 GHz frequency-switched radiometer, calibration method, retrieval procedure and error characterization are described. A comparison between our measurements and co-located CO measurements from the satellite sensors ACE-FTS on Scisat (v2.2), MLS on Aura (v3-3), MIPAS on Envisat (V3O_CO_12 + 13 and V4O_CO_200) and SMR on Odin (v225 and v021) is done. Our instrument, OSO, and the four satellite instruments show the same general variation of the vertical distribution of mesospheric CO in both the annual cycle and in shorter time period events with high CO mixing ratios during winter and very low amounts during summer in the observed 55–85 km altitude range. During 2004–2008 the agreement of the OSO instrument and the satellite sensors ACE-FTS, MLS and MIPAS(200) is good in the altitude range 55–70 km. Above 70 km OSO show up to 25% higher CO column values compared to both ACE and MLS. For the time period 2002–2003 CO from MIPAS(12 + 13) is up to 60% lower than OSO between 55 and 70 km. Mesospheric CO from the two versions of SMR deviates up to ±65% when compared to OSO, but the analysis is based on only a few co-locations.

Beschreibung: Retrieval of tropospheric CO column from hyperspectral infrared sounders – application to four years of Aqua/AIRS and MetOp-A/IASI Atmospheric Measurement Techniques Discussions, 5, 3861-3908, 2012 Author(s): T. Thonat, C. Crevoisier, N. A. Scott, A. Chédin, T. Schuck, R. Armante, and L. Crépeau Four years of tropospheric integrated content of CO are retrieved from infrared hyperspectral observations of AIRS onboard Aqua and IASI onboard MetOp-A, for the period July 2007–June 2011. The retrieval method is based on a double differential approach that relies on the difference between brightness temperatures (BT) observed by the sounder and BT simulated by the 4A radiative transfer model on collocated ECMWF reanalyses, for several couples of channels located in the 4.7 μm CO band. AIRS and IASI give access to similar integrated contents of CO with a maximum sensitivity near 450 hPa and half a maximum between 200 and 750 hPa depending on the thermal contrast (i.e. the difference between the surface temperature and the temperature of the first pressure level). However, differences in their spectral and radiometric characteristics yield differences in the retrieval characteristics with AIRS selected couples of channels being more sensitive to surface characteristics. Moreover, IASI covers the whole CO absorption band, with a 3 times greater spectral resolution, giving access to channels presenting a 3 times higher signal to noise ratio. This results in a better precision and lower standard deviation of the IASI retrievals. Conservatively, comparisons with CARIBIC aircraft measurements yield a relative difference of 3.42% for IASI and 4.92% for AIRS. On average, AIRS and IASI retrievals are in very good agreement, showing the same seasonality, seasonal amplitudes, interannual variability and spatial distribution. The analysis of the monthly evolution of CO particularly highlights the strong influence of biomass burning on the evolution of CO in several tropical regions. In particular, a sharp increase in CO in 2010 in the southern tropics, especially over South America and South Africa, is observed, and is shown to be related to El Niño and to the Atlantic Multidecadal Oscillation.

Beschreibung: Consistency of long-term elemental carbon trends from thermal and optical measurements in the IMPROVE network Atmospheric Measurement Techniques Discussions, 5, 3837-3859, 2012 Author(s): L.-W. A. Chen, J. C. Chow, J. G. Watson, and B. A. Schichtel Decreasing trends of elemental carbon (EC) have been reported at US Interagency Monitoring of Protected Visual Environments (IMPROVE) network since 1990, consistent with the phase-in of cleaner engines, residential biomass burning technologies, and prescribed burning methods. The EC trends from the past decade are cautioned due to an upgrade of IMPROVE carbon analyzers and the thermal/optical analysis protocol since 2005. Filter reflectance (τ R ) values measured as part of the carbon analysis were retrieved from archived data and compared with EC for 65 sites with more complete records from 2000 to 2009. The EC-τ R relationships show only minor changes of EC quantified by the original and upgraded instruments for most of the IMPROVE samples. EC and τ R show universal decreasing trends across the US. The EC and τ R trends are correlated well, with national average downward trends of 4.5% and 4.1% (of the 2000–2004 baseline medians) per year, respectively. The consistency between independent EC and τ R trends adds to the weight-of-evidence that EC reductions are real rather than an artifact of the measurement process.

Beschreibung: Maintaining consistent traceability in high precision isotope measurements of CO 2 : verifying atmospheric trends of δ 13 C Atmospheric Measurement Techniques Discussions, 5, 4003-4040, 2012 Author(s): L. Huang, A. Chivulescu, D. Ernst, W. Zhang, and Y.-S. Lee Maintaining consistent traceability of high precision measurements of CO 2 isotopes is critical in being able to observe accurate atmospheric trends of δ 13 C (CO 2 ). Although a number of laboratories/organizations around the world have been involved in baseline measurements of atmospheric CO 2 isotopes for several decades, the reports on their traceability measures are rare. In this paper, a principle and an approach for the traceability maintenance of high precision isotope measurements (δ 13 C and δ 18 O) in atmospheric CO 2 is described. The uncertainties of the traceability have been estimated based on the history of annual calibrations over the last 10 yr. The overall uncertainties of CO 2 isotope measurements for individual ambient samples carried out by our program at Environment Canada are estimated (excluding the uncertainty associated with the sampling). The values are 0.02‰ and 0.05‰ in δ 13 C and δ 18 O, respectively, close to the WMO targets for data compatibility. The annual rate of change in δ 13 C of the primary anchor used in our program (which is the laboratory standard linking ambient measurements back to the primary VPDB scale) is close to zero (−0.0016 ± 0.0012‰ per year) over the period of 10 yr (2001–2011). The average annual decreasing rate of δ 13 C in air CO 2 measurements at Alert over the period from 1999 to 2010 has been confirmed and verified, which is −0.025 ± 0.003‰ per year. The total change of δ 13 C in the annual mean value during this period is ∼−0.27‰. The concept of "Big Delta" is introduced and its role in maintaining traceability of the isotope measurements is described and discussed extensively. Finally, the challenges and a strategy for maintaining traceability are also discussed and suggested.

Beschreibung: Effect of spectrally varying albedo of vegetation surfaces on shortwave radiation fluxes and direct aerosol forcing Atmospheric Measurement Techniques Discussions, 5, 4041-4076, 2012 Author(s): L. Zhu, J. V. Martins, and H. Yu This study develops an algorithm for the representation of large spectral variations of albedo over vegetation surfaces based on Moderate Resolution Imaging Spectrometer (MODIS) observations at 7 discrete channels centered at 0.47, 0.55, 0.67, 0.86, 1.24, 1.63, and 2.11 μm. The MODIS 7-channel observations miss several major features of vegetation albedo including the vegetation red edge near 0.7 μm and vegetation absorption features at 1.48 and 1.92 μm. We characterize these features by investigating aerosol forcing in different spectral ranges. We show that the correction at 0.7 μm is the most sensitive and important due to the presence of the red edge and strong solar radiation; the other two corrections are less sensitive due to the weaker solar radiation and strong atmospheric water absorption. Four traditional approaches for estimating the reflectance spectrum and the MODIS enhanced vegetation albedo (MEVA) are tested against various vegetation types: dry grass, green grass, conifer, and deciduous from the John Hopkins University (JHU) spectral library; aspens from the US Geological Survey (USGS) digital spectral library; and Amazon vegetation types. Compared to traditional approaches, MEVA improves the accuracy of the outgoing flux at the top of the atmosphere by over 60 W m −2 and aerosol forcing by over 10 W m −2 . Specifically, for Amazon vegetation types, MEVA can improve the accuracy of daily averaged aerosol forcing at equator at equinox by 3.7 W m −2 (about 70% of the aerosol forcing calculated with high spectral resolution surface reflectance). These improvements indicate that MEVA can contribute to vegetation covered regional climate studies, and help to improve understanding of climate processes and climate change.

Beschreibung: First quantitative bias estimates for tropospheric NO 2 columns retrieved from SCIAMACHY, OMI, and GOME-2 using a common standard Atmospheric Measurement Techniques Discussions, 5, 3953-3971, 2012 Author(s): H. Irie, K. F. Boersma, Y. Kanaya, H. Takashima, X. Pan, and Z. F. Wang For the intercomparison of tropospheric nitrogen dioxide NO 2 vertical column density (VCD) data from three different satellite sensors (SCIAMACHY, OMI, and GOME-2), we use a common standard to quantitatively evaluate the biases for the respective data sets. As the standard, a regression analysis using a single set of collocated ground-based Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) observations at several sites in Japan and China in 2006–2011 is adopted. Examination of various spatial coincidence criteria indicates that the slope of the regression line can be influenced by the spatial distribution of NO 2 over the area considered. While the slope varies systematically with the distance between the MAX-DOAS and satellite observation points around Tokyo in Japan, such a systematic dependence is not clearly seen and correlation coefficients are generally higher in comparisons at sites in China. On the basis of these results, we focus mainly on comparisons over China and best estimate the biases in SCIAMACHY, OMI, and GOME-2 data (TM4NO2A and DOMINO version 2 products) against the MAX-DOAS observations to be −5±14 %, −10±14 %, and +1±14 %, respectively, which are all small and insignificant. We suggest that these small biases now allow analyses combining these satellite data for air quality studies that are more systematic and quantitative than previously possible.

Beschreibung: Validation of IASI FORLI carbon monoxide retrievals using FTIR data from NDACC Atmospheric Measurement Techniques Discussions, 5, 3973-4002, 2012 Author(s): T. Kerzenmacher, B. Dils, N. Kumps, T. Blumenstock, C. Clerbaux, P.-F. Coheur, P. Demoulin, O. García, M. George, D. W. T. Griffith, F. Hase, J. Hadji-Lazaro, D. Hurtmans, N. Jones, E. Mahieu, J. Notholt, C. Paton-Walsh, U. Raffalski, T. Ridder, M. Schneider, C. Servais, and M. De Mazière Carbon monoxide (CO) is retrieved daily and globally from space-borne IASI radiance spectra using the Fast Optimal Retrievals on Layers for IASI (FORLI) software developed at the Université Libre de Bruxelles (ULB). The IASI CO total column product for 2008 from the most recent FORLI retrieval version (20100815) is evaluated using correlative CO profile products retrieved from ground-based solar absorption Fourier transform infrared (FTIR) observations at the following FTIR spectrometer sites from the Network for the Detection of Atmospheric Composition Change (NDACC): Ny Ålesund, Kiruna, Bremen, Jungfraujoch, Izaña and Wollongong. In order to have good statistics for the comparisons, we included all IASI data from the same day, within a 100 km radius around the ground-based stations. The individual ground-based data were adjusted to the lowest altitude of the co-located IASI CO profiles. To account for the different vertical resolutions and sensitivities of the ground-based and satellite measurements, the averaging kernels associated with the various retrieved products have been used to properly smooth coincident data products. It has been found that the IASI CO total column products compare well on average with the co-located ground-based FTIR total columns at the selected NDACC sites and that there is no significant bias for the mean values at all stations.

Beschreibung: Precise pointing knowledge for SCIAMACHY solar occultation measurements Atmospheric Measurement Techniques Discussions, 5, 3797-3835, 2012 Author(s): K. Bramstedt, S. Noël, H. Bovensmann, M. Gottwald, and J. P. Burrows We present a method to precisely determine the viewing direction for solar occultation instruments from scans over the solar disk . Basic idea is the fit of the maximum intensity during the scan, which corresponds to the center of the solar disk in the scanning direction. We apply this method to the solar occultation measurements of the satellite instrument SCIAMACHY, which scans the sun in elevation direction. The achieved precision is in most case below 0.6 mdeg, which corresponds to an tangent height error of about 34 m for individual occultation sequences. The deviation of the derived elevation angle from the geolocation information given along with the product has a seasonal cycle with an amplitude of 2.02 mdeg, which is in tangent height an amplitude of about 114 m. The mean elevation angle offset is −4.7 mdeg (266 m). SCIAMACHY's sun follower device controls the azimuth viewing direction during the occultation measurements. The mean azimuth direction has an error of about 1.5 mdeg, which is about 84 m in horizontal direction at the tangent point. We observe also a seasonal cycle of the azimuth mispointing with an amplitude of 2.4 mdeg, which is slightly increasing with time. The almost constant mean offset is 88 mdeg, which is about 5.0 km horizontal offset at the tangent point.

Beschreibung: Geophysical validation and long-term consistency between GOME-2/MetOp-A total ozone column and measurements from the sensors GOME/ERS-2, SCIAMACHY/ENVISAT and OMI/Aura Atmospheric Measurement Techniques Discussions, 5, 3019-3045, 2012 Author(s): M. E. Koukouli, D. S. Balis, D. Loyola, P. Valks, W. Zimmer, N. Hao, J.-C. Lambert, M. Van Roozendael, C. Lerot, and R. J. D. Spurr The main aim of the paper is to assess the consistency of five years of Global Ozone Monitoring Experiment-2/Metop-A (GOME-2) total ozone columns and the long-term total ozone satellite monitoring database already in existence through an extensive inter-comparison and validation exercise using as reference Brewer and Dobson ground-based measurements. The behaviour of the GOME-2 measurements is being weighed against that of GOME (1995–2011), Ozone Monitoring Experiment (OMI) (since 2004) and the Scanning Imaging Absorption spectroMeter for Atmospheric CartograpHY (SCIAMACHY) (since 2002) total ozone column products. Over the background truth of the ground-based measurements, the total ozone columns are inter-evaluated using a suite of established validation techniques; the GOME-2 time series follow the same patterns as those observed by the other satellite sensors and in particular, on the average, GOME-2 data underestimate GOME data by about 0.80%, and underestimate SCIAMACHY data by 0.37% with no seasonal dependence of the differences between GOME-2, GOME and SCIAMACHY. The latter is expected since the three data sets are based on similar DOAS algorithms. This underestimation of GOME-2 is within the uncertainty of the reference data used in the comparisons. Compared to the OMI sensor, on the average GOME-2 data underestimate OMI_DOAS (collection 3) data by 1.28%, without any significant seasonal dependence of the differences between them. The lack of seasonality might be expected since both GDP 4.4 and OMI_DOAS are DOAS-type algorithms and both consider the variability of the stratospheric temperatures in their retrievals. Compared to the OMI_TOMS (collection 3) data, no bias was found. We hence conclude that the GOME-2 total ozone columns are well suitable to continue the long-term global total ozone record with the accuracy needed for climate monitoring studies.

Beschreibung: Organic particle types by single-particle measurements using a time-of-flight aerosol mass spectrometer coupled with a light scattering module Atmospheric Measurement Techniques Discussions, 5, 3047-3077, 2012 Author(s): S. Liu, L. M. Russell, D. T. Sueper, and T. B. Onasch Chemical and physical properties of individual ambient aerosol particles can vary greatly, so measuring the chemical composition at the single-particle level is essential for understanding atmospheric sources and transformations. Here we describe 46 days of single-particle measurements of atmospheric particles using a time-of-flight aerosol mass spectrometer coupled with a light scattering module (LS-ToF-AMS). The light scattering module optically detects particles larger than 180 nm vacuum aerodynamic diameter (130 nm geometric diameter) (with size resolution of 5–10 defined as d Δ d at full width at half maximum) before they arrive at the chemical mass detector and then triggers the saving of single-particle mass spectra. 271 641 particles were detected and sampled during 237 h of sampling in single particle mode. By comparing the timing of light scattering and chemical ion signals for each particle, particle types were classified and their number fractions determined as follows: prompt vaporization (49%), delayed vaporization (7%), and null (44%). LS-ToF-AMS provided the first direct measurement of the size-resolved collection efficiency (CE) of ambient particles, with an approximate 50% number-based CE for particles above detection limit. Prompt and delayed vaporization particles (147 357 particles) were clustered based on similar organic mass spectra (using K -means algorithm) to result in three major clusters: highly oxidized particles (dominated by m/z 44), relatively less oxidized particles (dominated by m/z 43), and particles associated with fresh urban emissions. Each of the three organic clusters had limited chemical properties of other clusters, suggesting that all of the sampled organic particle types were internally mixed to some degree; however, the internal mixing was never uniform and distinct particle types existed throughout the study. Furthermore, the single particle mass spectra and diurnal variations of these clusters agreed well with mass-based components identified (using factor analysis) from simultaneous ensemble-averaged measurements, supporting the connection between ensemble-based factors and atmospheric particle sources and processes. Measurements in this study illustrate that LS-ToF-AMS provides unique information about organic particle types by number as well as mass.

Beschreibung: Ice hydrometeor profile retrieval algorithm for high frequency microwave radiometers: application to the CoSSIR instrument during TC4 Atmospheric Measurement Techniques Discussions, 5, 3117-3198, 2012 Author(s): K. F. Evans, J. R. Wang, D. O'C Starr, G. Heymsfield, L. Li, L. Tian, R. P. Lawson, A. J. Heymsfield, and A. Bansemer A Bayesian algorithm to retrieve profiles of cloud ice water content (IWC), ice particle size ( D me ), and relative humidity from millimeter-wave/submillimeter-wave radiometers is presented. The first part of the algorithm prepares an a priori file with cumulative distribution functions (CDFs) and empirical orthogonal functions (EOFs) of profiles of temperature, relative humidity, three ice particle parameters (IWC, D me , distribution width), and two liquid cloud parameters. The a priori CDFs and EOFs are derived from CloudSat radar reflectivity profiles and associated ECMWF temperature and relative humidity profiles combined with three cloud microphysical probability distributions obtained from in situ cloud probes. The second part of the algorithm uses the CDF/EOF file to perform a Bayesian retrieval with a hybrid technique that uses Monte Carlo integration (MCI) or, when too few MCI cases match the observations, uses optimization to maximize the posterior probability function. The very computationally intensive Markov chain Monte Carlo (MCMC) method also may be chosen as a solution method. The radiative transfer model assumes mixtures of several shapes of randomly oriented ice particles, and here random aggregates of hexagonal plates, spheres, and dendrites are used for tropical convection. A new physical model of stochastic dendritic snowflake aggregation is developed. The retrieval algorithm is applied to data from the Compact Scanning Submillimeter-wave Imaging Radiometer (CoSSIR) flown on the ER-2 aircraft during the Tropical Composition, Cloud and Climate Coupling (TC4) experiment in 2007. Example retrievals with error bars are shown for nadir profiles of IWC, D me , and relative humidity, and nadir and conical scan swath retrievals of ice water path and average D me . The ice cloud retrievals are evaluated by retrieving integrated 94 GHz backscattering from CoSSIR for comparison with the Cloud Radar System (CRS) flown on the same aircraft. The rms difference in integrated backscattering is around 3 dB over a 30 dB range. A comparison of CoSSIR retrieved and CRS measured reflectivity shows that CoSSIR has the ability to retrieve low-resolution ice cloud profiles in the upper troposphere.

Beschreibung: Level 1 algorithms for TANSO on GOSAT: processing and on-orbit calibrations Atmospheric Measurement Techniques Discussions, 5, 2959-3018, 2012 Author(s): A. Kuze, H. Suto, K. Shiomi, T. Urabe, M. Nakajima, J. Yoshida, T. Kawashima, Y. Yamamoto, and F. Kataoka The Thermal And Near infrared Sensor for carbon Observation Fourier-Transform Spectrometer (TANSO-FTS) onboard the Greenhouse gases Observing SATellite (GOSAT)(nicknamed "Ibuki") has been providing global space-borne observations of carbon dioxide (CO 2 ) and methane (CH 4 ) since 2009. In this paper, first, the most recent operational Level 1 algorithms to produce the spectral radiance from the acquired interferogram are described. Second, we will describe the on-orbit characteristics and calibrations of TANSO-FTS. Overall functions and performances such as signal to noise ratio and spectral resolution are within design objectives. Correction methods of small on-orbit degradations and anomalies, which have been found since the launch are described. Lastly, calibrations of TANSO Cloud and Aerosol Imager (TANSO-CAI) are summarized. However, the Level 1B algorithms of TANSO-CAI are not mentioned, here in this paper.

Beschreibung: A Cavity-Enhanced Differential Optical Absorption Spectroscopy instrument for measurement of BrO, HCHO, HONO and O 3 Atmospheric Measurement Techniques Discussions, 5, 3079-3115, 2012 Author(s): D. J. Hoch, J. Buxmann, H. Sihler, D. Pöhler, C. Zetzsch, and U. Platt The chemistry of the troposphere and specifically the global tropospheric ozone budget is affected by reactive halogen compounds like BrO or ClO. Bromine monoxide (BrO) plays an important role in the processes of ozone destruction, disturbance of NO x and HO x chemistry, oxidation of DMS, and the deposition of elementary mercury. In the troposphere BrO has been detected in polar regions, at salt lakes, in volcanic plumes, and in the marine boundary layer. For a better understanding of these processes instruments with high spatial resolution and high sensitivity are necessary. A Cavity Enhanced Differential Optical Absorption Spectroscopy (CE-DOAS) instrument was designed and applied. For the first time, such an instrument uses an UV-LED in the UV-wavelength range (325–365 nm) to identify BrO. In laboratory studies at the Atmospheric Chemistry Research Laboratory, University of Bayreuth, Germany, BrO, as well as HONO, HCHO, O 3 , and O 4 , could be reliable determined at detection limits (for five minutes integration time) of 20 ppt for BrO, 9.1 ppb for HCHO, 970 ppt for HONO, and 91 ppb for O 3 , respectively. The best detection limits for BrO (11 ppt), HCHO (5.1 ppb), HONO (490 ppt), and O 3 (59 ppb) were achieved for integration times of 81 min or less.

Beschreibung: Comparison of satellite microwave backscattering (ASCAT) and visible/near-infrared reflectances (PARASOL) for the estimation of aeolian aerodynamic roughness length in arid and semi-arid regions Atmospheric Measurement Techniques Discussions, 5, 2933-2957, 2012 Author(s): C. Prigent, C. Jiménez, and J. Catherinot Previous studies examined the possibility to estimate the aeolian aerodynamic roughness length from satellites, either from visible/near-infrared observations or from microwave backscattering measurements. Here we compare the potential of the two approaches and propose to merge the two sources of information to benefit from their complementary aspects, i.e. the high spatial resolution of the visible/near-infrared (PARASOL part of the A-Train) and the independence from atmospheric contamination of the active microwaves (ASCAT on board MetOp). A global map of the aeolian aerodynamic roughness length at 6 km resolution is derived, for arid and semi-arid regions. It shows very good consistency with the existing information on the properties of these surfaces. The dataset is available to the community, for use in atmospheric dust transport models.

Beschreibung: SCIAMACHY WFM-DOAS XCO 2 : comparison with CarbonTracker XCO 2 focusing on aerosols and thin clouds Atmospheric Measurement Techniques Discussions, 5, 2887-2931, 2012 Author(s): J. Heymann, O. Schneising, M. Reuter, M. Buchwitz, V. V. Rozanov, V. A. Velazco, H. Bovensmann, and J. P. Burrows Carbon dioxide (CO 2 ) is the most important greenhouse gas whose atmospheric loading has been significantly increased by anthropogenic activity leading to global warming. Accurate measurements and models are needed in order to reliably predict our future climate. This, however, has challenging requirements. Errors in measurements and models need to be identified and minimised. In this context, we present a comparison between satellite-derived column-averaged dry air mole fractions of CO 2 , denoted XCO 2 , retrieved from SCIAMACHY/ENVISAT using the WFM-DOAS algorithm, and output from NOAA's global CO 2 modelling and assimilation system CarbonTracker. We investigate to what extent differences between these two data sets are influenced by systematic retrieval errors due to aerosols and unaccounted clouds. We analyse seven years of SCIAMACHY WFM-DOAS version 2.1 retrievals (WFMDv2.1) using the latest version of CarbonTracker (version 2010). We investigate to what extent the difference between SCIAMACHY and CarbonTracker XCO 2 are temporally and spatially correlated with global aerosol and cloud data sets. For this purpose, we use a global aerosol data set generated within the European GEMS project, which is based on assimilated MODIS satellite data. For clouds, we use a data set derived from CALIOP/CALIPSO. We find significant correlations of the SCIAMACHY minus CarbonTracker XCO 2 difference with thin clouds over the Southern Hemisphere. The maximum temporal correlation we find for Darwin, Australia ( r 2 = 54%). Large temporal correlations with thin clouds are also observed over other regions of the Southern Hemisphere (e.g. 43% for South America and 31% for South Africa). Over the Northern Hemisphere the temporal correlations are typically much lower. An exception is India, where large temporal correlations with clouds and aerosols have also been found. For all other regions the temporal correlations with aerosol are typically low. For the spatial correlations the picture is less clear. They are typically low for both aerosols and clouds, but dependent on region and season, they may exceed 30% (the maximum value of 46% has been found for Darwin during September to November). Overall we find that the presence of thin clouds can potentially explain a significant fraction of the difference between SCIAMACHY WFMDv2.1 XCO 2 and CarbonTracker over the Southern Hemisphere. Aerosols appear to be less of a problem. Our study indicates that the quality of the satellite derived XCO 2 will significantly benefit from a reduction of scattering related retrieval errors at least for the Southern Hemisphere.