ALBERT

Description: Potential of the TROPOspheric Monitoring Instrument (TROPOMI) onboard the Sentinel-5 Precursor for the monitoring of terrestrial chlorophyll fluorescence Atmospheric Measurement Techniques Discussions, 7, 12545-12588, 2014 Author(s): L. Guanter, I. Aben, P. Tol, J. M. Krijger, A. Hollstein, P. Köhler, A. Damm, J. Joiner, C. Frankenberg, and J. Landgraf Global monitoring of sun-induced chlorophyll fluorescence (SIF) can improve our knowledge about the photosynthetic functioning of terrestrial ecosystems. The feasibility of SIF retrievals from spaceborne atmospheric spectrometers has been demonstrated by a number of studies in the last years. In this work, we investigate the potential of the upcoming TROPOspheric Monitoring Instrument (TROPOMI) onboard the Sentinel-5 Precursor satellite mission for SIF retrieval. TROPOMI will sample the 675–775 nm spectral window with a spectral resolution of 0.5 nm and a pixel size of 7 km × 7 km. We use an extensive set of simulated TROPOMI data in order to assess the uncertainty of single SIF retrievals and subsequent spatio-temporal composites. Our results illustrate the enormous improvement in SIF monitoring achievable with TROPOMI with respect to comparable spectrometers currently in-flight, such as the Global Ozone Monitoring Experiment-2 (GOME-2) instrument. We find that TROPOMI can reduce global uncertainties in SIF mapping by more than a factor 2 with respect to GOME-2, which comes together with an about 5-fold improvement in spatial sampling. Finally, we discuss the potential of TROPOMI to accurately map other important vegetation parameters, such as leaf photosynthetic pigments and proxies for canopy structure, which will complement SIF retrievals for a self-contained description of vegetation condition and functioning.

Description: Validation of first chemistry mode retrieval results from new limb- imaging FTS GLORIA with correlative MIPAS-STR observations Atmospheric Measurement Techniques Discussions, 7, 12691-12717, 2014 Author(s): W. Woiwode, O. Suminska-Ebersoldt, H. Oelhaf, M. Höpfner, G. V. Belyaev, A. Ebersoldt, F. Friedl-Vallon, J.-U. Grooß, T. Gulde, M. Kaufmann, A. Kleinert, M. Krämer, E. Kretschmer, T. Kulessa, G. Maucher, T. Neubert, C. Piesch, P. Preusse, M. Riese, H. Rongen, C. Sartorius, G. Schardt, A. Schönfeld, D. Schuettemeyer, M. K. Sha, F. Stroh, J. Ungermann, C. M. Volk, and J. Orphal We report first chemistry mode retrieval results from the new airborne limb- imaging infrared FTS (Fourier transform spectrometer) GLORIA and comparisons with observations by the conventional airborne limb- scanning infrared FTS MIPAS-STR. For GLORIA, the flights aboard the high-altitude research aircraft M55 Geophysica during the ESSenCe campaign (ESa Sounder Campaign 2011) were the very first in field deployment after several years of development. The simultaneous observations of GLORIA and MIPAS-STR during the flight on 16 December 2011 inside the polar vortex and under the conditions of optically partially transparent polar stratospheric clouds (PSCs) provided us the unique opportunity to compare the observations by two different infrared FTS generations directly. The retrieval results of temperature, HNO 3 , O 3 , H 2 O, CFC-11 and CFC-12 show reasonable agreement of GLORIA with MIPAS-STR and collocated in-situ observations. For the horizontally binned hyperspectral limb-images, the GLORIA sampling outnumbered the horizontal cross-track sampling of MIPAS-STR by up to one order of magnitude. Depending on the target parameter, typical vertical resolutions of 0.5 to 2.0 km were obtained for GLORIA and are typically by factors of 2 to 4 better compared to MIPAS-STR. While the improvement of the performance, characterisation and data processing of GLORIA are subject of ongoing work, the presented first results already demonstrate the considerable gain in sampling and vertical resolution achieved with GLORIA.

Description: Comparison of nitric oxide measurements in the mesosphere and lower thermosphere from ACE-FTS, MIPAS, SCIAMACHY, and SMR Atmospheric Measurement Techniques Discussions, 7, 12735-12794, 2014 Author(s): S. Bender, M. Sinnhuber, T. von Clarmann, G. Stiller, B. Funke, M. López-Puertas, J. Urban, K. Pérot, K. A. Walker, and J. P. Burrows We compare the nitric oxide measurements in the mesosphere and lower thermosphere (60 to 150 km) from four instruments: ACE-FTS, MIPAS, SCIAMACHY, and SMR. We use the daily zonal mean data in that altitude range for the years 2004–2010 (ACE-FTS), 2005–2012 (MIPAS), 2008–2012 (SCIAMACHY), and 2003–2012 (SMR). We first compare the data qualitatively with respect to the morphology, focussing on the major features, and then compare the time series directly and quantitatively. In three geographical regions, we compare the vertical density profiles on coincident measurement days. Since none of the instruments delivers continuous daily measurements in this altitude region, we carried out a multi-linear regression analysis. This regression analysis considers annual and semi-annual variability in form of harmonic terms and inter-annual variability by responding linearly to the solar Lyman-α radiation index and the geomagnetic Kp index. This analysis helps to find similarities and differences in the individual data sets with respect to the inter-annual variations caused by geomagnetic and solar variability. We find that the data sets are consistent and that they only disagree on minor aspects. SMR and ACE-FTS deliver the longest time series in the mesosphere and they both agree remarkably well. The shorter time series from MIPAS and SCIAMACHY also agree with them where they overlap. The data agree within ten to twenty percent when the number densities are large, but they can differ by 50 to 100% in some cases.

Description: GPS radio occultation with TerraSAR-X and TanDEM-X: sensitivity of lower troposphere sounding to the Open-Loop Doppler model Atmospheric Measurement Techniques Discussions, 7, 12719-12733, 2014 Author(s): F. Zus, G. Beyerle, S. Heise, T. Schmidt, and J. Wickert The Global Positioning System (GPS) radio occultation (RO) technique provides valuable input for numerical weather prediction and is considered as a data source for climate related research. Numerous studies outline the high precision and accuracy of RO atmospheric soundings in the upper troposphere and lower stratosphere. In this altitude region (8–25 km) RO atmospheric soundings are considered to be free of any systematic error. In the tropical (30° S–30° N) Lower (

Description: From rovers on the surface of Mars to Voyager 1 near the edge of the solar system, spacecraft regularly call home to Earth. For five decades, the Deep Space Network has been at the other end of the line.

Description: The newly named Nobelists kept alive work on gallium nitride until their successful innovations paved the way to practical devices.

Description: The discomforts of noise in working and living can be reduced only by a rational approach to acoustics problems when building houses and factories, writes the technical director of the Acoustics Laboratory at the Massachusetts Institute of Technology.

Description: Integrated circuits with nanomaterial components can revolutionize technology, but only if they can be economically fabricated in large numbers.

Description: The belt emerges as a fundamental climatic feature of atmospheric circulation patterns on a rotating and differentially heated planet. But locating its edges and discerning anthropogenic influences remain difficult research problems.

Description: By manipulating fluorescence, the three prizewinners brought the hidden machinery of living cells into view.

Description: Researchers maintain that excellence in science requires a long-term strategy, money, and closer interactions with the commercial sector.

Description: Nonnuclear states’ patience with weapons states’ inaction on disarmament is wearing thin.

Description: The expansion of the Department of Energy’s high-bandwidth linkage is a step toward a global network for the transfer of scientific information.

Description: A highly deformable elastic sphere may bounce poorly on land, but it will skip spectacularly on water.

Description: Evaluation of a 2-step thermal method for separating organic and elemental carbon for radiocarbon analysis Atmospheric Measurement Techniques Discussions, 7, 131-169, 2014 Author(s): U. Dusek, M. Monaco, M. Prokopiou, F. Gongriep, R. Hitzenberger, H. A. J. Meijer, and T. Röckmann We thoroughly characterized a system for thermal separation of organic carbon (OC) and elemental carbon (EC) for subsequent radiocarbon analysis. Different organic compounds as well as ambient aerosol filter samples were introduced into an oven system and combusted to CO 2 in pure O 2 . The main objective was to test which combustion times and temperatures are best suited to separate OC and EC. The final separation step for OC was combustion at 360 °C for 15 min. Combustion at this temperature proved enough to remove several organic test substances from the filter (including high molecular weight humic acid) but did not remove substantial amounts of EC. For isolation of EC, OC first needs to be completely removed from the filter. This was achieved by water extraction of the filter, followed by combustion of the water insoluble OC at 360 °C and combustion at an intermediate temperature step of 2 min at 450 °C. This last step removed the most refractory OC together with some EC. Finally, the remaining EC was combusted to CO 2 at 650 °C. The recovery of black carbon after the intermediate 450 °C step was approximately 80%. Several tests provided strong evidence that OC was removed efficiently during the intermediate temperature step: (i) brown carbon, indicative of refractory OC, was removed; (ii) the fraction modern of EC did not decrease significantly if the temperature of the intermediate step was further increased. Based on tests with various organic compounds, we estimated that charred organic carbon could contribute 4–8% to an elemental carbon sample that was isolated according to our method.

Description: Droplet activation of wet particles: development of the Wet CCN approach Atmospheric Measurement Techniques Discussions, 7, 257-292, 2014 Author(s): S. Nakao, S. R. Suda, M. Camp, M. D. Petters, and S. M. Kreidenweis Relationships between critical supersaturation required for activation and particle dry diameter have been the primary means for experimentally characterizing cloud condensation nuclei (CCN) activity; however, use of the dry diameter inherently limits the application to cases where the dry diameter can be used to accurately estimate solute volume. This study challenges the requirement and proposes a new experimental approach, Wet CCN, for studying CCN activity without the need for a drying step. The new approach directly measures Köhler curves under sub-saturated conditions. The experimental setup consists of a humidity-controlled differential mobility analyzer and a CCN counter; wet diameter equilibrated at known relative humidity is used to characterize CCN activity instead of the dry diameter. The experimental approach was validated against ammonium sulfate, glucose and non-spherical ammonium oxalate monohydrate. Further, the approach was applied to a mixture of non-spherical iodine oxide particles. The Wet CCN approach successfully determined the hygroscopicity of non-spherical particles by collapsing them into spherical, deliquesced droplets. We further show that the Wet CCN approach offers unique insights to the physical and chemical impacts of the aqueous phase on CCN activity; a potential application is to investigate the impact of evaporation/co-condensation of water-soluble semi-volatile species on CCN activity.

Description: DIAL measurement of lower tropospheric ozone over Saga (33.24° N, 130.29° E), Japan, and comparison with a chemsitry-climate model Atmospheric Measurement Techniques Discussions, 7, 171-194, 2014 Author(s): O. Uchino, T. Sakai, T. Nagai, I. Morino, T. Maki, M. Deushi, K. Shibata, M. Kajino, T. Kawasaki, T. Akaho, S. Takubo, H. Okumura, K. Arai, M. Nakazato, T. Matsunaga, T. Yokota, S. Kawakami, K. Kita, and Y. Sasano We have improved an ozone DIfferential Absorption Lidar (DIAL) system, originally developed in March 2010. The improved DIAL system consists of a Nd:YAG laser and a 2 m Raman cell filled with 8.1 × 10 5 Pa of CO 2 gas which generate four Stokes lines (276, 287, 299, and 312 nm) of stimulated Raman scattering, and two receiving telescopes with diameters of 49 and 10 cm. Using this system, 44 ozone profiles were observed in the 1–6 km altitude range over Saga (33.24° N, 130.29° E) in 2012. High ozone concentration layers were observed at around 2 km altitude during April and May. Ozone column amounts within the 1–6 km altitude range were almost constant from January to March, and increased from late April to July. From mid-July through August, ozone column amounts decreased greatly because of exchanges of continental and maritime air masses. Then in mid-September they increased again within 1–6 km, and subsequently decreased slowly, becoming almost constant by December. The Meteorological Research Institute's Chemistry-Climate Model version 2 (MRI-CCM2) successfully predicted most of these ozone variations with the following exceptions. MRI-CCM2 could not predict the high ozone-mixing ratios measured at around 2 km altitude on 5 May and 11 May, possibly in part because emissions were assumed in the model to be constant (climatological data were used). Ozone-mixing ratios predicted by MRI-CCM2 were low in the 2–6 km range on 7 July and high in the 1–4 km range on 19 July compared with those measured by DIAL.

Description: A newly identified calculation discrepancy of the Sunset semi-continuous carbon analyzer Atmospheric Measurement Techniques Discussions, 7, 377-399, 2014 Author(s): G. Zheng, Y. Cheng, K. He, F. Duan, and Y. Ma Sunset Semi-Continuous Carbon Analyzer (SCCA) is an instrument widely used for carbonaceous aerosol measurement. Despite previous validation work, here we identified a new type of SCCA calculation discrepancy caused by the default multi-point baseline correction method. When exceeding a certain threshold carbon load, multi-point correction could cause significant Total Carbon (TC) underestimation. This calculation discrepancy was characterized for both sucrose and ambient samples with three temperature protocols. For ambient samples, 22%, 36% and 12% TC was underestimated by the three protocols, respectively, with corresponding threshold being ~0, 20 and 25 μg C. For sucrose, however, such discrepancy was observed with only one of these protocols, indicating the need of more refractory SCCA calibration substance. The discrepancy was less significant for the NIOSH (National Institute for Occupational Safety and Health)-like protocol compared with the other two protocols based on IMPROVE (Interagency Monitoring of PROtected Visual Environments). Although the calculation discrepancy could be largely reduced by the single-point baseline correction method, the instrumental blanks of single-point method were higher. Proposed correction method was to use multi-point corrected data when below the determined threshold, while use single-point results when beyond that threshold. The effectiveness of this correction method was supported by correlation with optical data.

Description: Remote sensing of cloud top pressure/height from SEVIRI: analysis of ten current retrieval algorithms Atmospheric Measurement Techniques Discussions, 7, 401-473, 2014 Author(s): U. Hamann, A. Walther, B. Baum, R. Bennartz, L. Bugliaro, M. Derrien, P. Francis, A. Heidinger, S. Joro, A. Kniffka, H. Le Gléau, M. Lockhoff, H.-J. Lutz, J. F. Meirink, P. Minnis, R. Palikonda, R. Roebeling, A. Thoss, S. Platnick, P. Watts, and G. Wind The role of clouds remains the largest uncertainty in climate projections. They influence solar and thermal radiative transfer and the earth's water cycle. Therefore, there is an urgent need for accurate cloud observations to validate climate models and to monitor climate change. Passive satellite imagers measuring radiation at visible to thermal infrared wavelengths provide a wealth of information on cloud properties. Among others, the cloud top height (CTH) – a crucial parameter to estimate the thermal cloud radiative forcing – can be retrieved. In this paper we investigate the skill of ten current retrieval algorithms to estimate the CTH using observations from the Spinning Enhanced Visible and InfraRed Imager (SEVIRI) onboard Meteosat Second Generation (MSG). In the first part we compare the ten SEVIRI cloud top pressure (CTP) datasets with each other. The SEVIRI algorithms catch the latitudinal variation of the CTP in a similar way. The agreement is better in the extratropics than in the tropics. In the tropics multi-layer clouds and thin cirrus layers complicate the CTP retrieval, whereas good agreement is found for the cores of the deep convective system having a high optical depth. Furthermore, a good agreement between the algorithms is observed for trade wind cumulus and marine stratocumulus clouds. In the second part of the paper the SEVIRI retrievals are compared to CTH observations from the Cloud-Aerosol LIdar with Orthogonal Polarization (CALIOP) and Cloud Profiling Radar (CPR) instruments. It is important to note that the different measurement techniques cause differences in the retrieved CHT data. SEVIRI measures a radiatively effective CTH, while the CTH of the active instruments is derived from the return time of the emitted signal. Therefore some systematic diffrences are expected. On average the CTHs detected by the SEVIRI algorithms are 1.0 to 2.5 km lower than CALIOP observations, and the correlation coefficients between the SEVIRI and the CALIOP datasets range between 0.77 and 0.90. The mean CTH differences between the SEVIRI algorithms and CPR observations are smaller than for CALIOP ranging from −0.8 km to 0.6 km. The correlation coefficients of CPR and SEVIRI observations range between 0.82 and 0.89. To discuss the origin of the CTH deviation we elaborate the comparison for three cloud categories: optically thin and thick single layer as well as multi-layer clouds. For optically thick clouds the correlation coefficients between the SEVIRI and the reference datasets are usually above 0.95. For optically thin single layer clouds the correlation coefficients are still above 0.92. For this cloud category the SEVIRI algorithms yield CTHs that are lower than CALIOP but similar to CPR observations. Most challenging are the multi-layer clouds, where the correlation coefficients are for most algorithms between 0.6 and 0.8. Finally, we evaluate the performance of the SEVIRI retrievals for boundary layer clouds. While the CTH retrieval for this cloud type is relatively accurate, there are still considerable differences between the algorithms. These are related to uncertainties in and limited vertical resolution of the assumed temperature profiles in combination with the presence of temperature inversions, which lead to ambiguities in the CTH retrieval. Alternative approaches for the CTH retrieval of low clouds are discussed.

Description: Retrieval of δ 18 O and δD in atmospheric water vapour from ground-based FTIR Atmospheric Measurement Techniques Discussions, 7, 195-231, 2014 Author(s): N. V. Rokotyan, V. I. Zakharov, K. G. Gribanov, F.-M. Bréon, J. Jouzel, R. Imasu, M. Werner, M. Butzin, C. Petri, T. Warneke, and J. Notholt This paper investigates the possibility of retrieving isotopic composition of atmospheric water vapour from high-resolution ground based measurements of atmospheric transmittance spectra in the near-infrared region (4000–11 000 cm −1 ). Simulated measurements of atmospheric transmittance were analyzed in order to find clear spectral signatures of H 2 18 O, HDO and H 2 16 O. Appropriate signals of the species of interest were found and also identified in measured spectra recorded by ground-based Fourier transform infrared spectrometer (FTIR) at the Institute of Environmental Physics of Bremen University. A set of H 2 18 O, HDO and H 2 16 O spectroscopic windows is presented. Theoretical estimations of the retrieval precision indicate that spectra recorded by ground-based FTIR spectrometers can be used to measure the seasonal cycle of δ 18 O and δD in the atmosphere. Studying the influence of the a priori on retrieval results shows low sensitivity to a priori assumptions. Impact of the uncertainties in spectroscopic line parameters of water isotopologues on precision of the retrieval of δ 18 O and δD is investigated. Time series of δ 18 O retrieved from ground-based FTIR spectra are represented for the first time. Comparison with the results of ECHAM5-wiso isotopic general circulation model simulations demonstrates a good agreement for "summer" measurements. Conversely, the comparison of "winter" measurements and modeling result show a discrepancy that demonstrate worse agreement that may be connected with incorrect temperature dependence of spectroscopic parameters.

Description: Intercomparison of Hantzsch and fiber-laser-induced-fluorescence formaldehyde measurements Atmospheric Measurement Techniques Discussions, 7, 233-255, 2014 Author(s): J. Kaiser, X. Li, R. Tillmann, I. Acir, F. Rohrer, R. Wegener, and F. N. Keutsch Two gas-phase formaldehyde (HCHO) measurement techniques, a modified commercial wet-chemical instrument based on Hantzsch Fluorimetry and a custom-built instrument based on Fiber-Laser Induced Fluorescence (FILIF), were deployed at the atmospheric simulation chamber SAPHIR to compare the instruments' performances under a range of conditions. Thermolysis of para-HCHO and ozonolysis of 1-butene were used as HCHO sources, allowing for calculations of theoretical HCHO mixing ratios. Calculated HCHO mixing ratios are compared to measurements, and the two measurements are also compared. Experiments were repeated under dry and humid conditions (RH 〈 2% and RH 〉 60%) to investigate the possibility of a water artifact in the FILIF measurements. The ozonolysis of 1-butene also allowed for the investigation of an ozone artifact seen in some Hantzsch measurements in previous intercomparisons. Results show that under all conditions the two techniques are well correlated ( R 2 ≥ 0.997), and linear regression statistics show measurements agree with within stated uncertainty (15% FILIF + 5% Hantzsch). No water or ozone artifacts are identified.

Description: An experiment to measure raindrop collection efficiencies: influence of rear capture Atmospheric Measurement Techniques Discussions, 7, 509-539, 2014 Author(s): A. Quérel, P. Lemaitre, M. Monier, E. Porcheron, A. I. Flossmann, and M. Hervo The analysis of radioactive aerosol scavenged by rain after the Chernobyl accident highlights certain differences between the modelling studies and the environmental measurements. Part of these discrepancies can probably be attributed to uncertainties in the efficiencies used to calculate aerosol particle collection by raindrops, particularly drops with a diameter larger than one millimetre. In order to improve the issue of these uncertainties, an experimental study was performed to close the gaps still existing for this key microphysical parameter. In the present article, attention is first focused on the efficiency with which aerosol particles, in the accumulation mode are collected by raindrops with a diameter of 2 mm. The collections efficiencies measured for aerosol particle in the sub-micron range are quantitatively consistent with previous theoretical model developed by Beard (1974) and thus highlight the major role of rear capture in the submicron range.

Description: Water vapor retrieval from OMI visible spectra Atmospheric Measurement Techniques Discussions, 7, 541-567, 2014 Author(s): H. Wang, X. Liu, K. Chance, G. Gonzalez Abad, and C. Chan Miller There are distinct spectral features of water vapor in the wavelength range covered by the Ozone Monitoring Instrument (OMI) visible channel. Although these features are much weaker than those at longer wavelengths, they can be exploited to retrieve useful information about water vapor. They have an advantage in that their small optical depth leads to fairly simple interpretation as measurements of the total water vapor column density. We have used the Smithsonian Astrophysical Observatory (SAO)'s OMI operational retrieval algorithm to derive the Slant Column Density (SCD) of water vapor from OMI measurements using the 430–480 nm spectral region after extensive optimization of retrieval windows and parameters. The Air Mass Factor (AMF) is calculated using look-up tables of scattering weights and monthly mean water vapor profiles from the GEOS-5 assimilation products. We convert from SCD to Vertical Column Density (VCD) using the AMF and generate associated retrieval averaging kernels and shape factors. Our standard water vapor product has a median SCD of ~ 1.3 × 10 23 molecule cm −2 and a median relative uncertainty of ~ 11% in the tropics, about a factor of 2 better than that from a similar OMI algorithm but using narrower retrieval window. The corresponding median VCD is ~ 1.2 × 10 23 molecule cm −2 . We have also explored the sensitivities to various parameters and compared our results with those from the Moderate-resolution Imaging Spectroradiometer (MODIS) and the Aerosol Robotic NETwork (AERONET).

Description: Six years of high-precision quasi-continuous atmospheric greenhouse gas measurements at Trainou Tower (Orléans Forest, France) Atmospheric Measurement Techniques Discussions, 7, 569-604, 2014 Author(s): M. Schmidt, M. Lopez, C. Yver Kwok, C. Messager, M. Ramonet, B. Wastine, C. Vuillemin, F. Truong, B. Gal, E. Parmentier, O. Cloué, and P. Ciais Results from the Trainou tall tower measurement station installed in 2006, are presented for atmospheric measurements of CO 2 , CH 4 , N 2 O, SF 6 , CO, H 2 mole fractions and Radon-222 activity. Air is sampled from four sampling heights (180 m, 100 m, 50 m and 5 m) of the Trainou 200 m television tower in the Orléans forest in France (47°57'53'' N, 2°06'45'' E, 131 m a.s.l.). The station is equipped with a custom-build CO 2 analyzer (CARIBOU), which is based on a commercial NDIR analyser (Licor 6252), and a coupled gas chromatographic GC system equipped with ECD and FID (HP6890N, Agilent) and a reduction gas detector (PP1, Peak Performer). Air intakes, pumping and air drying system are shared between the CARIBOU and the GC systems. After some initial problems, we achieved short-term repeatability (1 sigma, over several days) for the GC system of of 0.05 ppm for CO 2 , 1.4 ppb for CH 4 , 0.25 ppb for N 2 O, 0.08 ppb for SF 6 , 0.88 ppb for CO and 3.8 for H 2 . The repeatability of the CARIBOU CO 2 analyser is 0.06 ppm. In addition to the in-situ measurements, weekly flask sampling is performed, and flask air samples are analysed at the LSCE central laboratory for the same species as well for stable isotopes of CO 2 . The comparison between in-situ measurements and the flask sampling showed averaged differences of 0.08 ± 1.4 ppm CO 2 , 0.69 ± 7.3 ppb CH 4 , 0.64 ± 0.62 ppb N 2 O, 0.01 ± 0.1 ppt SF 6 and 1.5 ± 5.3 ppb CO for the years 2008–2012. At Trainou station, the mean annual increase rates from 2007 to 2011 at the 180 m sampling height were 2.2 ppm yr −1 for CO 2 , 4 ppb yr −1 for CH 4 , 0.78 ppb yr −1 for N 2 O and 0.29 ppt yr −1 for SF6 respectively. For all species the 180 m sampling level showed the smallest diurnal variation. Mean diurnal gradients between the 50 m and the 180 m sampling level reached up to 30 ppm CO 2 , 15 ppm CH 4 or 0.5 ppb N 2 O during night whereas the mean gradients are smaller than 0.5 ppm for CO 2 and 1.5 ppb for CH 4 during afternoon.

Description: A DOAS-like method for total column of CO 2 from ground-based FTS measurements of the direct solar beam Atmospheric Measurement Techniques Discussions, 7, 2405-2423, 2014 Author(s): Y. F. Huo, M. Z. Duan, and W. S. Tian A new algorithm, similar to that of DOAS method, is developed to retrieve the total column CO 2 from the ground-based hyper-spectral measurements of direct solar beam. Other than spectrum fitting method, which is generally used in the optimal estimation algorithm, the radiances ratio at two wavelength named channel pair, where one is of weak and the other is of relatively strong absorption, is used to retrieve the total column CO 2 in the Short Wave InfraRed(SWIR) band. Sensitivity studies show that this DOAS-like method is less dependent on the model parameters such as aerosols, water vapor, surface pressure, temperature, wavelength shift and signal noise, and the pairs of channels are carefully selected based on the sensitivity studies. To validate the algorithm, the FTS measurements located at Xi'Chong astronomical observatory are used to derive the total column CO 2 amount, 272 pairs ratios are used in the retrieval and the results agree very well with that of GOSAT, which shows that the DOAS-like method could give reasonable value of X CO 2 .

Description: On sampling uncertainty of satellite ozone profile measurements Atmospheric Measurement Techniques Discussions, 7, 2381-2403, 2014 Author(s): V. F. Sofieva, N. Kalakoski, S.-M. Päivärinta, J. Tamminen, E. Kyrölä, M. Laine, and L. Froidevaux Satellite measurements sample continuous fields of atmospheric constituents at discrete locations and times. However, insufficient or inhomogeneous sampling, if not taken into account, can result in inaccurate average estimates and even induce spurious features. We propose to characterize the spatio-temporal inhomogeneity of atmospheric measurements by a measure, which is a linear combination of the asymmetry and entropy of a sampling distribution. It is shown that this measure is related to the so-called sampling uncertainty, which occurs due to non-uniform sampling patterns. We have estimated the sampling uncertainty of zonal mean ozone profiles for six limb-viewing satellite instruments participating in the European Space Agency Ozone Climate Change Initiative project using the high-resolution ozone field simulated with the FinROSE chemistry-transport model. It is shown that the sampling uncertainty for the instruments with coarse sampling is not negligible and can be as large as a few percent. It is found that the standard deviation of the sampling uncertainty in the monthly zonal mean data allows for a simple parameterization in terms of the product of the standard deviation of natural variations and the proposed inhomogeneity measure. The focus of this work is the vertical ozone distributions measured by limb-viewing satellite instruments, but the developed methods can also be applied to different satellite, ground-based and in-situ measurements.

Description: Validation of GOMOS ozone precision estimates in the stratosphere Atmospheric Measurement Techniques Discussions, 7, 2459-2490, 2014 Author(s): V. F. Sofieva, J. Tamminen, E. Kyrölä, A. Laeng, T. von Clarmann, F. Dalaudier, A. Hauchecorne, J.-L. Bertaux, G. Barrot, L. Blanot, D. Fussen, and F. Vanhellemont Accurate information about uncertainties is required in nearly all data analyses (inter-comparisons, data assimilation, combined use, etc.). Validation of precision estimates (viz., the random component of estimated uncertainty) is important for remote sensing measurements, which provide the information about atmospheric parameters via solving an inverse problem. For the Global Ozone Monitoring by Occultation of Stars (GOMOS) instrument, it is of a real challenge, due to dependence of signal-to-noise ratio (and thus precision estimates) on stellar properties, small number of self-collocated measurements, and uncertainty estimates growing with time due to instrument ageing. Estimated uncertainties of ozone retrievals are small in the stratosphere for bright stars, which results in additional complexity of detecting them on the background of natural ozone variability. In this paper, we discuss different methods for geophysical validation of precision estimates and their applicability to GOMOS data. We propose a simple method for validation of GOMOS precision estimates for ozone in the stratosphere. This method is based on comparisons of difference in sample variance with the difference in uncertainty estimates for measurements from different stars selected in a region of small natural variability. For GOMOS, the difference in sample variances for different stars at altitudes 25–45 km is well explained by the difference in squared precisions, if stars are not dim. Since it is observed for several stars, and since normalized χ 2 is close to 1 in these occultations in the stratosphere, we can conclude that GOMOS precision estimates are realistic in occultations of sufficiently bright stars. For dim stars, errors are overestimated due to improper accounting for the dark charge correction uncertainty in the error budget. The proposed method can also be applied to stratospheric ozone data from other instruments, including multi-instrument analyses.

Description: The next generation of low-cost personal air quality sensors for quantitative exposure monitoring Atmospheric Measurement Techniques Discussions, 7, 2425-2457, 2014 Author(s): R. Piedrahita, Y. Xiang, N. Masson, J. Ortega, A. Collier, Y. Jiang, K. Li, R. Dick, Q. Lv, M. Hannigan, and L. Shang Advances in embedded systems and low-cost gas sensors are enabling a new wave of low cost air quality monitoring tools. Our team has been engaged in the development of low-cost wearable air quality monitors (M-Pods) using the Arduino platform. The M-Pods use commercially available metal oxide semiconductor (MO x ) sensors to measure CO, O 3 , NO 2 , and total VOCs, and NDIR sensors to measure CO 2 . MO x sensors are low in cost and show high sensitivity near ambient levels; however they display non-linear output signals and have cross sensitivity effects. Thus, a quantification system was developed to convert the MO x sensor signals into concentrations. Two deployments were conducted at a regulatory monitoring station in Denver, Colorado. M-Pod concentrations were determined using laboratory calibration techniques and co-location calibrations, in which we place the M-Pods near regulatory monitors to then derive calibration function coefficients using the regulatory monitors as the standard. The form of the calibration function was derived based on laboratory experiments. We discuss various techniques used to estimate measurement uncertainties. A separate user study was also conducted to assess personal exposure and M-Pod reliability. In this study, 10 M-Pods were calibrated via co-location multiple times over 4 weeks and sensor drift was analyzed with the result being a calibration function that included drift. We found that co-location calibrations perform better than laboratory calibrations. Lab calibrations suffer from bias and difficulty in covering the necessary parameter space. During co-location calibrations, median standard errors ranged between 4.0–6.1 ppb for O 3 , 6.4–8.4 ppb for NO 2 , 0.28–0.44 ppm for CO, and 16.8 ppm for CO 2 . Median signal to noise ( S/N ) ratios for the M-Pod sensors were higher for M-Pods than the regulatory instruments: for NO 2 , 3.6 compared to 23.4; for O 3 , 1.4 compared to 1.6; for CO, 1.1 compared to 10.0; and for CO 2 , 42.2 compared to 300–500. The user study provided trends and location-specific information on pollutants, and affected change in user behavior. The study demonstrated the utility of the M-Pod as a tool to assess personal exposure.

Description: Verification and application of the extended Spectral Deconvolution Algorithm (SDA+) methodology to estimate aerosol fine and coarse mode extinction coefficients in the marine boundary layer Atmospheric Measurement Techniques Discussions, 7, 2545-2584, 2014 Author(s): K. C. Kaku, J. S. Reid, N. T. O'Neill, P. K. Quinn, D. J. Coffman, and T. F. Eck The Spectral Deconvolution Algorithm (SDA) and SDA+ (extended SDA) methodologies can be employed to separate the fine and coarse mode extinction coefficients from measured total aerosol extinction coefficients, but their common use is currently limited to AERONET Aerosol Optical Depth (AOD). Here we provide the verification of the SDA+ methodology on a non-AERONET aerosol product, by applying it to fine and coarse mode nephelometer and Particle Soot Absorption Photometer (PSAP) data sets collected in the marine boundary layer. Using datasets collected on research vessels by NOAA PMEL, we demonstrate that with accurate input, SDA+ is able to predict the fine and coarse mode scattering and extinction coefficient partition in global data sets representing a range of aerosol regimes. However, in low-extinction regimes commonly found in the clean marine boundary layer, SDA+ output accuracy is sensitive to instrumental calibration errors. This work was extended to the calculation of coarse and fine mode scattering coefficients with similar success. This effort not only verifies the application of the SDA+ method to in situ data, but by inference verifies the method as a whole for a host of applications, including AERONET. Study results open the door to much more extensive use of nephelometers and PSAPs, with the ability to calculate fine and coarse mode scattering and extinction coefficients in field campaigns that do not have the resources to explicitly measure these values.

Description: What is the benefit of ceilometers for aerosol remote sensing? An answer from EARLINET Atmospheric Measurement Techniques Discussions, 7, 2491-2543, 2014 Author(s): M. Wiegner, F. Madonna, I. Binietoglou, R. Forkel, J. Gasteiger, A. Geiß, G. Pappalardo, K. Schäfer, and W. Thomas With the establishment of ceilometer networks by national weather services a discussion commenced to which extent these simple backscatter lidars can be used for aerosol research. Though primarily designed for the detection of clouds it was shown that at least observations of the vertical structure of the boundary layer might be possible. However, an assessment of the potential of ceilometers for the quantitative retrieval of aerosol properties is still missing. In this paper we discuss different retrieval methods to derive the aerosol backscatter coefficient β p with special focus on the calibration of the ceilometers. Different options based on forward and backward integration methods are compared with respect to their accuracy and applicability. It is shown, that advanced lidar systems as being operated in the framework of EARLINET are excellent tools for the calibration, so that aerosol retrievals based on forward integration can readily be implemented. Furthermore, we discuss uncertainties introduced by incomplete overlap, the unknown lidar ratio, and water vapor absorption. The latter is relevant for the very large number of ceilometers operating in the spectral range around λ = 905 nm. Nevertheless, the retrieval of β p with an relative error in the order of 10% seems feasible, so ceilometer networks can provide useful information to fill the spatial gaps between sophisticated lidar systems. As a consequence several international projects are underway to harmonize data sets from different ceilometer and lidar networks for the sake of providing near real time information for weather prediction and air quality issues.

Description: Ionospheric assimilation of radio occultation and ground-based GPS data using non-stationary background model error covariance Atmospheric Measurement Techniques Discussions, 7, 2631-2661, 2014 Author(s): C. Y. Lin, T. Matsuo, J. Y. Liu, C. H. Lin, H. F. Tsai, and E. A. Araujo-Pradere Ionospheric data assimilation is a powerful approach to reconstruct the 3-D distribution of the ionospheric electron density from various types of observations. We present a data assimilation model for the ionosphere, based on the Gauss–Markov Kalman filter with the International Reference Ionosphere (IRI) as the background model, to assimilate two different types of total electron content (TEC) observations from ground-based GPS and space-based FORMOSAT-3/COSMIC (F3/C) radio occultation. Covariance models for the background model error and observational error play important roles in data assimilation. The objective of this study is to investigate impacts of stationary (location-independent) and non-stationary (location-dependent) classes of the background model error covariance on the quality of assimilation analyses. Location-dependent correlations are modeled using empirical orthogonal functions computed from an ensemble of the IRI outputs, while location-independent correlations are modeled using a Gaussian function. Observing System Simulation Experiments suggest that assimilation of TEC data facilitated by the location-dependent background model error covariance yields considerably higher quality assimilation analyses. Results from assimilation of real ground-based GPS and F3/C radio occultation observations over the continental United States are presented as TEC and electron density profiles. Validation with the Millstone Hill incoherent scatter radar data and comparison with the Abel inversion results are also presented. Our new ionospheric data assimilation model that employs the location-dependent background model error covariance outperforms the earlier assimilation model with the location-independent background model error covariance, and can reconstruct the 3-D ionospheric electron density distribution satisfactorily from both ground- and space-based GPS observations.

Description: Calibrating airborne measurements of airspeed, pressure and temperature using a Doppler laser air-motion sensor Atmospheric Measurement Techniques Discussions, 7, 2585-2630, 2014 Author(s): W. A. Cooper, S. M. Spuler, M. Spowart, D. H. Lenschow, and R. B. Friesen A new laser air-motion sensor measures the true airspeed with an uncertainty of less than 0.1 m s −1 (standard error) and so reduces uncertainty in the measured component of the relative wind along the longitudinal axis of the aircraft to about the same level. The calculated pressure expected from that airspeed at the inlet of a pitot tube then provides a basis for calibrating the measurements of dynamic and static pressure, reducing standard-error uncertainty in those measurements to less than 0.3 hPa and the precision applicable to steady flight conditions to about 0.1 hPa. These improved measurements of pressure, combined with high-resolution measurements of geometric altitude from the Global Positioning System, then indicate (via integrations of the hydrostatic equation during climbs and descents) that the offset and uncertainty in temperature measurement for one research aircraft are +0.3 ± 0.3 °C. For airspeed, pressure and temperature these are significant reductions in uncertainty vs. those obtained from calibrations using standard techniques. Finally, it is shown that the new laser air-motion sensor, combined with parametrized fits to correction factors for the measured dynamic and ambient pressure, provides a measurement of temperature that is independent of any other temperature sensor.

Description: An inverse modelling approach for frequency response correction of capacitive humidity sensors in ABL research with small unmanned aircraft Atmospheric Measurement Techniques Discussions, 7, 4407-4438, 2014 Author(s): N. Wildmann, F. Kaufmann, and J. Bange The measurement of water-vapour concentration in the atmosphere is an ongoing challenge in environmental research. Satisfactory solutions are present for ground-based meteorological stations and measurements of mean values. However, advanced research of thermodynamic processes also aloft, above the surface layer and especially in the atmospheric boundary layer (ABL), requires the resolution of small-scale turbulence. Sophisticated optical instruments are used in airborne meteorology with manned aircraft to achieve the necessary fast response measurements in the order of 1 Hz (e.g. LiCor 7500). Since these instruments are too large and heavy for the application on the promising platforms of small remotely piloted aircraft (RPA), a method is presented in this study, that enhances small capacitive humidity sensors to be able to resolve turbulent eddies in the order of 10 m. For this purpose a physical and dynamical model of such a sensor is described and inverted in order to restore original water vapour fluctuations from sensor measurements. Examples of flight measurements show how the method can be used to correct vertical profiles and resolve turbulence spectra up to about 3 Hz.

Description: Improving the bias characteristics of the ROPP refractivity and bending angle operators Atmospheric Measurement Techniques Discussions, 7, 4439-4480, 2014 Author(s): C. P. Burrows, S. B. Healy, and I. D. Culverwell The bending angle observation operator (forward model) currently used to assimilate radio occultation (RO) data at the Met Office, ECMWF and other centres is the same as is included in the Radio Occultation Processing Package (ROPP), along with the corresponding tangent-linear and adjoint code. The functionality of this package is described in another paper in this issue. The mean bending angle innovations produced with this operator using Met Office background fields show a bias that oscillates with height and whose magnitude peaks between the model levels. These oscillations have been attributed to shortcomings in the assumption of exponentially varying refractivity between model levels. This is used directly in the refractivity operator, and indirectly to produce forward-modelled bending angles via the Abel transform. When the spacing between the model levels is small, this assumption is acceptable, but at stratospheric heights where the model level spacing is large, these biases can be significant, and can potentially degrade analyses. This paper provides physically-based improvements to the functional form of refractivity with height. These new assumptions considerably improve the oscillatory bias, and a number of approaches for practical implementation of the bending angle operator are provided.

Description: New algorithm for integration between wireless microwave sensor network and radar for improved rainfall measurement and mapping Atmospheric Measurement Techniques Discussions, 7, 4481-4528, 2014 Author(s): Y. Liberman, R. Samuels, P. Alpert, and H. Messer One of the main challenges for meteorological and hydrological modelling is accurate rainfall measurement and mapping across time and space. To date the most effective methods for large scale rainfall estimates are radar, satellites, and more recently, received signal level (RSL) measurements received from commercial microwave networks (CMN). While these methods provide improved spatial resolution over traditional rain gauges, these have their limitations as well. For example, the wireless CMN, which are comprised of microwave links (ML), are dependant upon existing infrastructure, and the ML arbitrary distribution in space. Radar, on the other hand, is known in its limitation in accurately estimating rainfall in urban regions, clutter areas and distant locations. In this paper the pros and cons of the radar and ML methods are considered in order to develop a new algorithm for improving rain fall measurement and mapping, which is based on data fusion of the different sources. The integration is based on an optimal weighted average of the two data sets, taking into account location, number of links, rainfall intensity and time step. Our results indicate that by using the proposed new method we not only generate a more accurate 2-D rainfall reconstructions, compared with actual rain intensities in space, but also the reconstructed maps are extended to the maximum coverage area. By inspecting three significant rain events, we show an improvement of rain rate estimation over CMN or radar alone, almost uniformly, both for instantaneous spatial measurements, as well as in calculating total accumulated rainfall. These new improved 2-D rainfall maps, and the accurate rainfall measurements over large areas at sub-hourly time scales, will allow for improved understanding, initialization and calibration of hydrological and meteorological models necessary, mainly, for water resource management and planning.

Description: First results from a rotational Raman scattering cloud algorithm applied to the Suomi National Polar-orbiting Partnership (NPP) Ozone Mapping Profiler Spectrometer (OMPS) nadir mapper Atmospheric Measurement Techniques Discussions, 7, 2689-2714, 2014 Author(s): A. Vasilkov, J. Joiner, and C. Seftor This paper reports initial results from an Ozone Mapping Profiler Suite (OMPS) nadir mapper cloud pressure and cloud fraction algorithm. The OMPS cloud products are intended for use in OMPS ozone or other trace-gas algorithms. We developed the OMPS cloud products using a heritage algorithm developed for the Ozone Monitoring Instrument (OMI) on NASA's Aura satellite. The cloud pressure algorithm utilizes the filling-in of ultra-violet solar Fraunhofer lines by rotational Raman scattering. The OMPS cloud products are evaluated by comparison with OMI cloud products that have been compared in turn with other collocated satellite data including cloud optical thickness profiles derived from a combination of measurements from the CloudSat radar and the MODIS imaging radiometer. We find that the probability density functions (PDFs) of effective cloud fraction retrieved from OMPS and OMI measurements are very similar. The PDFs of the OMPS and OMI cloud pressures are comparable. However, OMPS retrieves somewhat higher pressures on average. The current NASA total ozone retrieval algorithm makes use of a monthly gridded cloud pressure climatology developed from OMI. This climatology captures much of the variability associated with the relevant cloud pressures. However, the use of actual cloud pressures retrieved with OMPS in place of the OMI climatology appears to improve OMPS total column ozone estimates slightly.

Description: Using self organising maps to explore ozone profile validation results – SCIAMACHY limb compared to ground-based lidar observations Atmospheric Measurement Techniques Discussions, 7, 4373-4406, 2014 Author(s): J. A. E. van Gijsel, R. Zurita-Milla, P. Stammes, S. Godin-Beekmann, T. Leblanc, M. Marchand, I. S. McDermid, K. Stebel, W. Steinbrecht, and D. P. J. Swart Traditional validation of atmospheric profiles is based on the intercomparison of two or more datasets in predefined ranges or classes of a given observational characteristic such as latitude or solar zenith angle. In this study we train a self organizing map (SOM) with a full time series of relative difference profiles of SCIAMACHY limb v5.02 and lidar ozone profiles from seven observation sites. Each individual observation characteristic is then mapped to the obtained SOM to investigate to which degree variation in this characteristic is explanatory for the variation seen in the SOM map. For the studied datasets, altitude-dependent relations for the global dataset were found between the difference profiles and studied variables. From the lowest altitude studied (18 km) ascending, the most influencing factors were found to be longitude, followed by solar zenith angle and latitude, sensor age and again solar zenith angle together with the day of the year at the highest altitudes studied here (up to 45 km). Clustering into three classes showed that there are also some local dependencies, with for instance one cluster having a much stronger correlation with the sensor age (days since launch) between 36 and 42 km. It was shown that the proposed approach provides a powerful tool for the exploring of differences between datasets without being limited to a-priori defined data subsets.

Description: A new differential absorption lidar to measure sub-hourly fluctuation of tropospheric ozone profiles in the Baltimore–Washington DC region Atmospheric Measurement Techniques Discussions, 7, 4321-4371, 2014 Author(s): J. T. Sullivan, T. J. McGee, G. K. Sumnicht, L. W. Twigg, and R. M. Hoff Tropospheric ozone profiles have been retrieved from the new ground based National Aeronautics and Space Administration (NASA) Goddard Space Flight Center TROPospheric OZone DIfferential Absorption Lidar (GSFC TROPOZ DIAL) in Greenbelt, MD (38.99° N, 76.84° W, 57 m a.s.l.) from 400 m to 12 km a.g.l. Current atmospheric satellite instruments cannot peer through the optically thick stratospheric ozone layer to remotely sense boundary layer tropospheric ozone. In order to monitor this lower ozone more effectively, the Tropospheric Ozone Lidar Network (TOLNet) has been developed, which currently consists of five stations across the US. The GSFC TROPOZ DIAL is based on the Differential Absorption Lidar (DIAL) technique, which currently detects two wavelengths, 289 and 299 nm. Ozone is absorbed more strongly at 289 nm than at 299 nm. The DIAL technique exploits this difference between the returned backscatter signals to obtain the ozone number density as a function of altitude. The transmitted wavelengths are generated by focusing the output of a quadrupled Nd:YAG laser beam (266 nm) into a pair of Raman cells, filled with high pressure hydrogen and deuterium. Stimulated Raman Scattering (SRS) within the focus generates a significant fraction of the pump energy at the first Stokes shift. With the knowledge of the ozone absorption coefficient at these two wavelengths, the range resolved number density can be derived. An interesting atmospheric case study involving the Stratospheric–Tropospheric Exchange (STE) of ozone is shown to emphasize the regional importance of this instrument as well as assessing the validation and calibration of data. The retrieval yields an uncertainty of 16–19% from 0–1.5 km, 10–18% from 1.5–3 km, and 11–25% from 3 km to 12 km. There are currently surface ozone measurements hourly and ozonesonde launches occasionally, but this system will be the first to make routine tropospheric ozone profile measurements in the Baltimore–Washington DC area.

Description: Mixing layer height retrieval with ceilometer and Doppler lidar: from case studies to long-term assessment Atmospheric Measurement Techniques Discussions, 7, 4275-4319, 2014 Author(s): J. H. Schween, A. Hirsikko, U. Löhnert, and S. Crewell Aerosol signatures observed by ceilometers are frequently used to derive mixing layer height (MLH) which is an essential variable for air quality modeling. Doppler wind lidar measurements of vertical velocity can provide a more direct estimation of MLH via simple thresholding. A case study reveals difficulties in the aerosol based MLH retrieval during transition times when the mixing layer is built up in the morning and when turbulence decays in the afternoon. The differences can be explained by the fact that the aerosol distribution is related to the history of the mixing process and aerosol characteristics are modified by humidification. The results of the case study are generalized by evaluating one year of joint measurements by a Vaisala CT25K and a HALO Photonics Streamline wind lidar. On average the aerosol based retrieval gives higher MLH than the wind lidar with an overestimation of MLH by about 300 m (600 m) in the morning (late afternoon). When turbulence is fully developed around noon best agreement is found between both methods. This diurnal behavior is even more pronounced in fair weather conditions classified by less than 4 octa. In these conditions the mean diurnal cycle of cloud base height corresponds well to the mixing layer height showing potential for a simplified MLH estimation.

Description: Innovation and excellence are the buzzwords.

Description: A bicameral spending agreement should also smooth the upcoming fiscal year 2015 appropriations process.

Description: With the help of techniques first used by particle physicists decades ago, scientists and archivists are preserving our precious aural heritage.

Description: In the past two decades, a flourishing economy and maturing infrastructure have Taiwanese physicists both staying home more and engaging internationally.

Description: Red dwarfs are the Milky Way’s most common stars. And their smallness helps those who hunt for Earth-like planets.

Description: To be worthy of the title “scientific,” a law of nature must be testable. But nothing requires a scientific law to be unchanging.

Description: Quantitative infrared absorption cross-sections of isoprene for atmospheric measurements Atmospheric Measurement Techniques Discussions, 7, 4163-4189, 2014 Author(s): C. S. Brauer, T. A. Blake, A. B. Guenther, R. L. Sams, and T. J. Johnson Isoprene (C 5 H 8 , 2-methyl-1,3-butadiene) is a volatile organic compound (VOC) that is one of the primary contributors to annual global VOC emissions. Produced by vegetation as well as anthropogenic sources, the OH- and O 3 -initiated oxidations of isoprene are a major source of atmospheric oxygenated organics. Few quantitative infrared studies have been reported for isoprene, however, limiting the ability to quantify isoprene emissions via stand-off infrared or in situ detection. We thus report absorption coefficients and integrated band intensities for isoprene in the 600–6500 cm −1 region. The pressure-broadened (1 atmosphere N 2 ) spectra were recorded at 278, 298 and 323 K in a 19.94 cm path length cell at 0.112 cm −1 resolution, using a Bruker 66v FTIR. Composite spectra are derived from a minimum of seven isoprene sample pressures at each temperature and the number densities are normalized to 296 K and 1 atmosphere.

Description: Re-construction of global solar radiation time series from 1933 to 2013 at the Izaña Atmospheric Observatory Atmospheric Measurement Techniques Discussions, 7, 4191-4227, 2014 Author(s): R. D. García, E. Cuevas, O. E. García, V. E. Cachorro, P. Pallé, J. J. Bustos, P. M. Romero-Campos, and A. M. de Frutos This paper presents the re-construction of the 80 year time series of daily global shortwave downward radiation (SDR) at the subtropical high-mountain Izaña Atmospheric Observatory (IZO, Spain). For this purpose, we combine SDR estimates from sunshine duration (SD) data using the Ångström–Prescott method over the 1933/1991 period, and SDR observations directly performed by pyranometers between 1992 and 2013. Since SDR measurements have been used as a reference, a strict quality control has been applied, when it was not possible data have been re-calibrated by using the LibRadtran model. By comparing to high quality SDR measurements, the precision and consistency over time of SDR estimations from SD data have successfully been documented. We obtain a overall root mean square error (RMSE) of 9.2% and an agreement between the variances of SDR estimations and SDR measurements within 92% (correlation coefficient of 0.96). Nonetheless, this agreement significantly increases when the SDR estimation is done considering different daily fractions of clear sky (FCS). In that case, RMSE is reduced by half, up to about 4.5%, when considering percentages of FCS 〉 40% (90% of days in the testing period). Furthermore, we prove that the SDR estimations can monitor the SDR anomalies in consistency with SDR measurements and, then, can be suitable for re-constructing solar radiation time series. The re-constructed IZO global SDR time series between 1933 and 2013 confirms discontinuities and periods of increases/decreases of solar radiation at Earth's surface observed at a global scale, such as the early brightening, dimming and brightening. This fact supports the consistency of the IZO SDR time series presented in this work, which may be a reference for solar radiation studies in the subtropical North Atlantic region.

Description: Adaptive neuro fuzzy inference system for profiling of the atmosphere Atmospheric Measurement Techniques Discussions, 7, 2715-2736, 2014 Author(s): K. Ramesh, A. P. Kesarkar, J. Bhate, M. Venkat Ratnam, and A. Jayaraman Retrieval of accurate profiles of temperature and water vapor is important for the study of atmospheric convection. However, it is challenging because of the uncertainties associated with direct measurement of atmospheric parameters during convection events using radiosonde and retrieval of remote-sensed observations from satellites. Recent developments in computational techniques motivated the use of adaptive techniques in the retrieval algorithms. In this work, we have used the Adaptive Neuro Fuzzy Inference System (ANFIS) to retrieve profiles of temperature and humidity over tropical station Gadanki (13.5° N, 79.2° E), India. The observations of brightness temperatures recorded by Radiometrics Multichannel Microwave Radiometer MP3000 for the period of June–September 2011 are used to model profiles of atmospheric parameters up to 10 km. The ultimate goal of this work is to use the ANFIS forecast model to retrieve atmospheric profiles accurately during the wet season of the Indian monsoon (JJAS) season and during heavy rainfall associated with tropical convections. The comparison analysis of the ANFIS model retrieval of temperature and relative humidity (RH) profiles with GPS-radiosonde observations and profiles retrieved using the Artificial Neural Network (ANN) algorithm indicates that errors in the ANFIS model are less even in the wet season, and retrievals using ANFIS are more reliable, making this technique the standard. The Pearson product movement correlation coefficient ( r ) between retrieved and observed profiles is more than 99% for temperature profiles for both techniques and therefore both techniques are successful in the retrieval of temperature profiles. However, in the case of RH the retrieval using ANFIS is found to be better. The comparison of mean absolute error (MAE), root mean square error (RMSE) and symmetric mean absolute percentage error (SMAPE) of retrieved temperature and RH profiles using ANN and ANFIS also indicates that profiles retrieved using ANFIS are significantly better compared to the ANN technique. The error analysis of profiles concludes that retrieved profiles using ANFIS techniques have improved the retrievals substantially; however, retrieval of RH by both techniques (ANN and ANFIS) has limited success.

Description: The ability to probe phonon–surface scattering could help elucidate the curious thermal behavior of some nanostructured materials.

Description: Automated rain rate estimates using the Ka-band ARM Zenith Radar (KAZR) Atmospheric Measurement Techniques Discussions, 7, 1807-1833, 2014 Author(s): A. Chandra, C. Zhang, P. Kollias, S. Matrosov, and W. Szyrmer The use of millimeter wavelength radars for probing precipitation has recently gained interest. However, estimation of precipitation variables is not straightforward due to strong attenuation, radar receiver saturation, antenna wet radome effects and natural microphysical variability. Here, an automated algorithm is developed for routinely retrieving rain rates from profiling Ka-band (35-GHz) ARM zenith radars (KAZR). A 1-D simple, steady state microphysical model is used to estimate the impact of microphysical processes and attenuation on the profiles of the radar observables at 35-GHz and thus provide criteria for identifying when attenuation or microphysical processes dominate KAZR observations. KAZR observations are also screened for saturation and wet radome effects. The proposed algorithm is implemented in two steps: high rain rates are retrieved by using the amount of attenuation in rain layers, while lower rain rates by the Z e – R (reflectivity-rain rate) relation is implemented. Observations collected by the KAZR, disdrometer and scanning weather radars during the DYNAMO/AMIE field campaign at Gan Island of the tropical Indian Ocean are used to validate the proposed approach. The results indicate that the proposed algorithm can be used to derive robust statistics of rain rates in the tropics from KAZR observations.

Description: Determination and analysis of spectral aerosol optical properties by a multi-instrumental approach Atmospheric Measurement Techniques Discussions, 7, 1871-1916, 2014 Author(s): S. Segura, V. Estellés, G. Titos, H. Lyamani, M. P. Utrillas, P. Zotter, A. S. H. Prévôt, G. Močnik, L. Alados-Arboledas, and J. A. Martínez-Lozano Continuous in-situ measurements of aerosol optical properties where conducted from 20 June to 20 July in Granada (Spain) with a 7-wavelength Aethalometer, a Multi Angle Absorption Photometer, and a 3-wavelength integrating Nephelometer. The aim of this work is to describe a methodology to obtain the absorption coefficients ( b abs ) for the different Aethalometer wavelengths. In this way, data have been compensated using algorithms which best estimate the compensation factors needed. Two empirical factors are used to infer the absorption coefficients from the Aethalometer measurements: C – the parameter describing the enhancement of absorption by particles in the filter matrix due to multiple scattering of light in the filter matrix; and f – the parameter compensating for non-linear loading effects in the filter matrix. Spectral dependence of f found in this study is not very strong. Values for the campaign lie in the range from 1.15 at 370 nm to 1.11 at 950 nm. Wavelength dependence in C proves to be more important, and also more difficult to calculate. The values obtained span from 3.40 at 370 nm to 4.35 at 950 nm. Furthermore, the temporal evolution of the Ångström exponent of absorption (α abs ) and the single scattering albedo (ω 0 ), is presented. On average α abs is around 1.1 ± 0.3, and ω 0 is 0.78 ± 0.08 and 0.74 ± 0.09 at 370 and 950 nm, respectively. These are typical values for sites with a predominance of absorbing particles, and the urban measurement site in this study is such. The b abs average values are of 16 ± 10 Mm −1 (at 370 nm) and 5 ± 3 Mm −1 (at 950 nm), respectively. Finally, differences between working days and Sunday have been further analyzed, obtaining higher b abs and lower ω 0 during week than on Sundays as a consequence of the influence of diesel traffic.

Description: HCOOH measurements from space: TES retrieval algorithm and observed global distribution Atmospheric Measurement Techniques Discussions, 7, 1975-2015, 2014 Author(s): K. E. Cady-Pereira, S. Chaliyakunnel, M. W. Shephard, D. B. Millet, M. Luo, and K. C. Wells Presented is a detailed description of the TES-Aura satellite formic acid (HCOOH) retrieval algorithm and initial results quantifying the global distribution of tropospheric HCOOH. The retrieval strategy, including the optimal estimation methodology, spectral microwindows, a priori constraints, and initial guess information, are provided. A comprehensive error and sensitivity analysis is performed in order to characterize the retrieval performance, degrees of freedom for signal, vertical resolution, and limits of detection. These results show that the TES HCOOH retrievals: (i) typically provide at best 1.0 pieces of information, (ii) have the most vertical sensitivity in the range from 900 to 600 hPa with ~ 2 km vertical resolution, (iii) require at least 0.5 ppbv of HCOOH for detection if thermal contrast is greater than 10 K, and higher concentrations as thermal contrast decreases; and (iv) based on an ensemble of simulated retrievals, are unbiased with a standard deviation of ±0.3 ppbv. Globally, the spatial distribution of tropospheric HCOOH derived from TES is broadly consistent with that simulated by a state-of-the-science chemical transport model (GEOS-Chem CTM). However, TES HCOOH is frequently higher than is predicted by GEOS-Chem, and this is in agreement with recent work pointing to a large missing source of atmospheric HCOOH. The model bias is especially pronounced over biomass burning regions, suggesting that fires are one key source of the missing atmospheric HCOOH in the model.

Description: Variable anisotropy of small-scale stratospheric irregularities retrieved from stellar scintillation measurements by GOMOS/Envisat Atmospheric Measurement Techniques Discussions, 7, 1275-1304, 2014 Author(s): V. Kan, V. F. Sofieva, and F. Dalaudier In this paper, we consider possibilities for studying the anisotropy of small-scale air density irregularities using satellite observations of bi-chromatic stellar scintillations during tangential occultations. Estimation of the anisotropy coefficient (the ratio of the characteristic horizontal to vertical scales) and other atmospheric parameters is based on the comparison of simulated/theoretical and experimental auto-spectra and coherency spectra of scintillation. Our analyses exploit a 3-D model of the spectrum of atmospheric inhomogeneities, which consists of anisotropic and isotropic components. For the anisotropic component, a spectral model with variable anisotropy is used. Using stellar scintillation measurements by GOMOS (Global Ozone Monitoring by Occultation of Stars) fast photometers, estimates of the anisotropy coefficient are obtained for atmospheric irregularities with vertical scales of 8–55 m at altitudes of 43–30 km. It is shown that the anisotropy increases from about 10 to 50 with increasing vertical scales.

Description: Application of a GC-ECD for measurements of biosphere–atmosphere exchange fluxes of peroxyacetyl nitrate using the relaxed eddy accumulation and gradient method Atmospheric Measurement Techniques Discussions, 7, 1917-1974, 2014 Author(s): A. Moravek, T. Foken, and I. Trebs Peroxyacetyl nitrate (PAN) may constitute a significant fraction of reactive nitrogen in the atmosphere. Current knowledge about the biosphere–atmosphere exchange of PAN is limited and only few studies have investigated the deposition of PAN to terrestrial ecosystems. We developed a flux measurement system for the determination of biosphere–atmosphere exchange fluxes of PAN using both the hyperbolic relaxed eddy accumulation (HREA) method and the modified Bowen ratio (MBR) method. The system consists of a modified, commercially available gas chromatograph with electron capture detection (GC-ECD, Meteorologie Consult GmbH, Germany). Sampling was performed by trapping PAN onto two pre-concentration columns; during HREA operation one was used for updraft and one for downdraft events and during MBR operation the two columns allowed simultaneous sampling at two measurement heights. The performance of the PAN flux measurement system was tested at a natural grassland site, using fast response ozone (O 3 ) measurements as a proxy for both methods. The measured PAN fluxes were comparatively small (daytime PAN deposition was on average −0.07 nmol m −2 s −1 and, thus, prone to significant uncertainties. A major challenge in the design of the system was the resolution of the small PAN mixing ratio differences. Consequently, the study focuses on the performance of the analytical unit and a detailed analysis of errors contributing to the overall uncertainty. The error of the PAN mixing ratio differences ranged from 4 to 15 ppt during the MBR and between 18 and 26 ppt during the HREA operation, while during daytime measured PAN mixing ratios were of similar magnitude. Choosing optimal settings for both the MBR and HREA method, the study shows that the HREA method did not have a significant advantage towards the MBR method under well mixed conditions as it was expected.

Description: Development of a cavity enhanced aerosol albedometer Atmospheric Measurement Techniques Discussions, 7, 2981-3019, 2014 Author(s): W. Zhao, X. Xu, M. Dong, W. Chen, X. Gu, C. Hu, Y. Huang, X. Gao, W. Huang, and W. Zhang We report on the development of a cavity enhanced aerosol single scattering albedometer incorporating incoherent broad-band cavity-enhanced spectroscopy (IBBCEAS) approach and an integrating sphere (IS) for simultaneous in situ measurements of aerosol scattering and extinction coefficients in the exact same sample volume. The cavity enhanced albedometer employed a blue light-emitting diode (LED) based IBBCEAS approach for the measurement of wavelength-resolved aerosol optical extinction over the spectral range of 445–480 nm. An integrating sphere nephelometer coupled to the IBBCEAS setup was used for the measurement of aerosol scattering. The scattering signal was measured with a single channel photomultiplier tube (PMT), providing an integrated value over a narrow bandwidth (FWHM ~ 9 nm) in the spectral region of 465–474 nm. A scattering coefficient at a wavelength of 470 nm was deduced as an averaged scattering value and used for data analysis and instrumental performance comparison. Performance evaluation of the albedometer was carried out using laboratory-generated particles and ambient aerosol. The scattering and extinction measurements of monodisperse polystyrene latex (PSL) spheres generated in laboratory proved excellent correlation between two channels of the albedometer. The retrieved refractive index (RI) from the measured scattering and extinction efficiencies agreed well with the values reported in previously published papers. Aerosol light scattering and extinction coefficients, single scattering albedo (SSA) and NO 2 concentrations in an ambient sample were directly and simultaneously measured using the developed albedometer. The developed instrument was validated via an intercomparison of the measured aerosol scattering coefficient and NO 2 trace concentration against a TSI 3563 integrating nephelometer and a chemiluminescence detector, respectively.

Description: Optimized method for black carbon analysis in ice and snow using the Single Particle Soot Photometer Atmospheric Measurement Techniques Discussions, 7, 3075-3111, 2014 Author(s): I. A. Wendl, J. A. Menking, R. Färber, M. Gysel, S. D. Kaspari, M. J. G. Laborde, and M. Schwikowski In this study we attempt to optimize the method for measuring black carbon (BC) in snow and ice using a single particle soot photometer (SP2). Beside the previously applied ultrasonic (CETAC) and Collison-type nebulizers we introduce a jet (APEX-Q) nebulizer to aerosolize the aqueous sample for SP2 analysis. Both CETAC and APEX-Q require small sample volumes (few milliliters) which makes them suitable for ice core analysis. The APEX-Q shows the least size-dependent nebulizing efficiency in the BC particle diameter range of 100–1000 nm. The CETAC has the advantage that air and liquid flows can be monitored continuously. All nebulizer-types require a calibration with BC standards for the determination of the BC mass concentration in unknown aqueous samples. We found Aquadag to be a suitable material for preparing calibration standards. Further, we studied the influence of different treatments for fresh discrete snow and ice samples as well as the effect of storage. The results show that samples are best kept frozen until analysis. Once melted, they should be sonicated for 25 min, immediately analyzed while being stirred and not be refrozen.

Description: Total column water vapour measurements from GOME-2 MetOp-A and MetOp-B Atmospheric Measurement Techniques Discussions, 7, 3021-3073, 2014 Author(s): M. Grossi, P. Valks, D. Loyola, B. Aberle, S. Slijkhuis, T. Wagner, S. Beirle, and R. Lang The knowledge of the total column water vapour (TCWV) global distribution is fundamental for climate analysis and weather monitoring. In this work, we present the retrieval algorithm used to derive the operational TCWV from the GOME-2 sensors and perform an extensive inter-comparison and validation in order to estimate their absolute accuracy and long-term stability. We use the recently reprocessed data sets retrieved by the GOME-2 instruments aboard EUMETSAT's MetOp-A and MetOp-B satellites and generated by DLR in the framework of the O3M-SAF using the GOME Data Processor (GDP) version 4.7. The retrieval algorithm is based on a classical Differential Optical Absorption Spectroscopy (DOAS) method and combines H 2 O/O 2 retrieval for the computation of the trace gas vertical column density. We introduce a further enhancement in the quality of the H 2 O column by optimizing the cloud screening and developing an empirical correction in order to eliminate the instrument scan angle dependencies. We evaluate the overall consistency between about 8 months measurements from the newer GOME-2 instrument on the MetOp-B platform with the GOME-2/MetOp-A data in the overlap period. Furthermore, we compare GOME-2 results with independent TCWV data from ECMWF and with SSMIS satellite measurements during the full period January 2007–August 2013 and we perform a validation against the combined SSM/I + MERIS satellite data set developed in the framework of the ESA DUE GlobVapour project. We find global mean biases as small as ± 0.03 g cm −2 between GOME-2A and all other data sets. The combined SSM/I-MERIS sample is typically drier than the GOME-2 retrievals (−0.005 g cm −2 ), while on average GOME-2 data overestimate the SSMIS measurements by only 0.028 g cm −2 . However, the size of some of these biases are seasonally dependent. Monthly average differences can be as large as 0.1 g cm −2 , based on the analysis against SSMIS measurements, but are not as evident in the validation with the ECMWF and the SSM/I + MERIS data. Studying two exemplary months, we estimate regional differences and identify a very good agreement between GOME-2 total columns and all three independent data sets, especially for land areas, although some discrepancies over ocean and over land areas with high humidity and a relatively large surface albedo are also present.

Description: Aerosol optical and microphysical retrievals from a hybrid multiwavelength lidar dataset – DISCOVER-AQ 2011 Atmospheric Measurement Techniques Discussions, 7, 3113-3157, 2014 Author(s): P. Sawamura, D. Müller, R. M. Hoff, C. A. Hostetler, R. A. Ferrare, J. W. Hair, R. R. Rogers, B. E. Anderson, L. D. Ziemba, A. J. Beyersdorf, K. L. Thornhill, E. L. Winstead, and B. N. Holben Retrievals of aerosol microphysical properties (e.g. effective radius, volume and surface-area concentrations) and aerosol optical properties (e.g. complex index of refraction and single scattering albedo) were obtained from a hybrid multiwavelength lidar dataset for the first time. In July of 2011, in the Baltimore-Washington DC region, synergistic profiling of optical and microphysical properties of aerosols with both airborne in-situ and ground-based remote sensing systems was performed during the first deployment of DISCOVER-AQ. The hybrid multiwavelength lidar dataset combines elastic ground-based measurements at 355 nm with airborne High Spectral Resolution Lidar (HSRL) measurements at 532 nm and elastic measurements at 1064 nm that were obtained less than 5 km apart of each other. This was the first study in which optical and microphysical retrievals from lidar were obtained during the day and directly compared to AERONET and in-situ measurements for 11 cases. Good agreement was observed between lidar and AERONET retrievals. Larger discrepancies were observed between lidar retrievals and in-situ measurements obtained by the aircraft and aerosol hygroscopic effects are believed to be the main factor of such discrepancies.

Description: In October 2012 Felix Baumgartner fell farther and faster than anyone before him. The forces he experienced during his flight can be readily analyzed, thanks to the GPS data collected during his jump.