ALBERT

Description: Space-borne observation of methane from atmospheric infrared sounder version 6: validation and implications for data analysis Atmospheric Measurement Techniques Discussions, 8, 8563-8597, 2015 Author(s): X. Xiong, F. Weng, Q. Liu, and E. Olsen Atmospheric Methane (CH 4 ) is generated as a standard product in recent version of the hyperspectral Atmospheric Infrared Sounder (AIRS-V6) aboard NASA's Aqua satellite at the NASA Goddard Earth Sciences Data and Information Services Center (NASA/GES/DISC). Significant improvements in AIRS-V6 was expected but without a thorough validation. This paper first introduced the improvements of CH 4 retrieval in AIRS-V6 and some characterizations, then presented the results of validation using ~ 1000 aircraft profiles from several campaigns spread over a couple of years and in different regions. It was found the mean biases of AIRS CH 4 at layers 343–441 and 441–575 hPa are −0.76 and −0.05 % and the RMS errors are 1.56 and 1.16 %, respectively. Further analysis demonstrates that the errors in the spring and in the high northern latitudes are larger than in other seasons or regions. The error is correlated with Degree of Freedoms (DOFs), particularly in the tropics or in the summer, and cloud amount, suggesting that the "observed" spatiotemporal variation of CH 4 by AIRS is imbedded with some artificial impact from the retrieval sensitivity in addition to its variation in reality, so the variation of information content in the retrievals needs to be taken into account in data analysis of the retrieval products. Some additional filtering (i.e. rejection of profiles with obvious oscillation as well as those deviating greatly from the norm) for quality control is recommended for the users to better utilize AIRS-V6 CH 4 , and their implementation in the future versions of the AIRS retrieval algorithm is under consideration.

Description: Impact of aerosols on the OMI tropospheric NO 2 retrievals over industrialized regions: how accurate is the aerosol correction of cloud-free scenes via a simple cloud model? Atmospheric Measurement Techniques Discussions, 8, 8385-8437, 2015 Author(s): J. Chimot, T. Vlemmix, J. P. Veefkind, J. F. de Haan, and P. F. Levelt The Ozone Monitoring Instrument (OMI) instrument has provided daily global measurements of tropospheric NO 2 for more than a decade. Numerous studies have drawn attention to the complexities related to measurements of tropospheric NO 2 in the presence of aerosols. Fine particles affect the OMI spectral measurements and the length of the average light path followed by the photons. However, they are not explicitly taken into account in the current OMI tropospheric NO 2 retrieval chain. Instead, the operational OMI O 2 -O 2 cloud retrieval algorithm is applied both to cloudy scenes and to cloud free scenes with aerosols present. This paper describes in detail the complex interplay between the spectral effects of aerosols, the OMI O 2 -O 2 cloud retrieval algorithm and the impact on the accuracy of the tropospheric NO 2 retrievals through the computed Air Mass Factor (AMF) over cloud-free scenes. Collocated OMI NO 2 and MODIS Aqua aerosol products are analysed over East China, in industrialized area. In addition, aerosol effects on the tropospheric NO 2 AMF and the retrieval of OMI cloud parameters are simulated. Both the observation-based and the simulation-based approach demonstrate that the retrieved cloud fraction linearly increases with increasing Aerosol Optical Thickness (AOT), but the magnitude of this increase depends on the aerosol properties and surface albedo. This increase is induced by the additional scattering effects of aerosols which enhance the scene brightness. The decreasing effective cloud pressure with increasing AOT represents primarily the absorbing effects of aerosols. The study cases show that the actual aerosol correction based on the implemented OMI cloud model results in biases between −20 and −40 % for the DOMINO tropospheric NO 2 product in cases of high aerosol pollution (AOT ≥ 0.6) and elevated particles. On the contrary, when aerosols are relatively close to the surface or mixed with NO 2 , aerosol correction based on the cloud model results in overestimation of the DOMINO tropospheric NO 2 product, between 10 and 20 %. These numbers are in line with comparison studies between ground-based and OMI tropospheric NO 2 measurements under conditions with high aerosol pollution and elevated particles. This highlights the need to implement an improved aerosol correction in the computation of tropospheric NO 2 AMFs.

Description: Sensitivity of thermal infrared sounders to the chemical and micro-physical properties of UTLS secondary sulphate aerosols Atmospheric Measurement Techniques Discussions, 8, 8439-8481, 2015 Author(s): P. Sellitto and B. Legras Monitoring upper tropospheric-lower stratospheric (UTLS) secondary sulphate aerosols and their chemical and micro-physical properties from satellite nadir observations is crucial to better understand their formation and evolution processes and then to estimate their impact to the UTLS chemistry, and on regional and global radiative balance. Here we present a study aimed at the evaluation of the sensitivity of thermal infrared (TIR) satellite nadir observations to the chemical composition and the size distribution of idealized UTLS sulphate aerosol layers. The extinction properties of sulphuric acid/water droplets, for different sulphuric acid mixing ratios and temperatures, are systematically analysed. The extinction coefficients are derived by means of a Mie code, using refractive indexes taken from the GEISA (Gestion et Étude des Informations Spectroscopiques Atmosphériques: Management and Study of Spectroscopic Information) spectroscopic database and log-normal size distributions with different effective radii and number concentrations. IASI (Infrared Atmospheric Sounding Interferometer) pseudo-observations are generated using forward radiative transfer calculations performed with the 4A (Automatized Atmospheric Absorption Atlas) radiative transfer model, to estimate the impact of the extinction of idealized aerosol layers, at typical UTLS conditions, on the brightness temperature spectra observed by this satellite instrument. We found a marked and typical spectral signature of these aerosol layers between 700 and 1200 cm −1 , due to the absorption bands of the sulphate and bi-sulphate ions and the undissociated sulphuric acid, with the main absorption peaks at 1170 and 905 cm −1 . The dependence of the aerosol spectral signature to the sulphuric acid mixing ratio, and effective number concentration and radius, as well as the role of interferring parameters like the ozone, sulphur dioxide, carbon dioxide and ash absorption, and temperature and water vapour profile uncertainties, are analyzed and critically discussed.

Description: Global cloud top height retrieval using SCIAMACHY limb spectra: model studies and first results Atmospheric Measurement Techniques Discussions, 8, 8295-8352, 2015 Author(s): K.-U. Eichmann, L. Lelli, C. von Savigny, H. Sembhi, and J. P. Burrows Cloud top heights (CTH) were retrieved for the period 1 January 2003 to 7 April 2012 using height-resolved limb spectra measured with the Scanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) on board ENVISAT (ENVIronmental SATellite). In this study, we tested the sensitivity of the colour index method used in the retrieval code SCODA (SCIAMACHY Cloud Detection Algorithm) and the accuracy of the retrieved CTHs in comparison to other methods. Sensitivity studies using the radiative transfer model SCIATRAN showed that the method is capable of generally detecting cloud tops down to about 5 km and very thin cirrus clouds even up to the tropopause. Volcanic particles can also be detected that occasionally reach the lower stratosphere. Low clouds at 2–3 km can only be retrieved under very clean atmospheric conditions, as light scattering of aerosols interferes with the cloud retrieval. Upper tropospheric ice clouds are detectable for cloud optical depths down to about τ N = 0.005, which is in the subvisual range. The detection sensitivity decreases towards the surface. An optical thickness of roughly 0.1 was the lower detection limit for water cloud top heights at 5 km. This value is much lower than thresholds reported for the passive cloud detection in nadir viewing direction. Comparisons with SCIAMACHY nadir cloud top heights, calculated with the Semi-Analytical CloUd Retrieval Algorithm (SACURA), showed a good agreement in the global cloud field distribution. But only opaque clouds (τ N 〉 5) are detectable with the nadir passive retrieval technique in the UV-visible and infrared wavelength range. So due to the frequent occurrence of thin and sub-visual cirrus clouds in the tropics, large cloud top height deviations were detected between both viewing geometries. Also the land/sea contrast seen in nadir retrievals was not detected in limb mode. Co-located cloud top height measurements of the limb viewing Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on ENVISAT for the period from January 2008 to March 2012 were compared, showing good agreement to within 1 km, which is smaller than the vertical field of view of both instruments. Lower stratospheric aerosols from volcanic eruptions occasionally interfered with the cloud retrieval and inhibited detection of tropospheric clouds. Examples of the impact of these events are shown for the volcanoes Kasatochi in August 2008, Sarychev Peak in June 2009, and Nabro in June 2010. Long-lasting aerosol layers were detected after these events in the Northern Hemisphere down to the tropics. Particle top heights up to about 22 km were retrieved in 2009, when the enhanced lower stratospheric aerosol layer persisted for about 7 months. Up to about 82 % of the Northern hemispheric lower stratosphere between 30° and 70° was covered by scattering particles in August 2009 and nearly half in October 2008.

Description: Operation of the Airmodus A11 nano Condensation Nucleus Counter at various inlet pressures, various operation temperatures and design of a new inlet system Atmospheric Measurement Techniques Discussions, 8, 8483-8508, 2015 Author(s): J. Kangasluoma, A. Franchin, J. Duplissy, L. Ahonen, F. Korhonen, M. Attoui, J. Mikkilä, K. Lehtipalo, J. Vanhanen, M. Kulmala, and T. Petäjä Measuring sub-3 nm particles outside of controlled laboratory conditions is a challenging task, as many of the instruments are operated at their limits and are subjected to changing ambient conditions. In this study, we advance the current understanding on the operation of Airmodus A11 nano Condensation Nucleus Counter (nCNC), which consists of a A10 Particle Size Magnifier (PSM) and A20 condensation particle counter (CPC). We explore the effect of the inlet line pressure on the measured particle concentration. We identify two different regions inside the instrument where supersaturation of working fluid can take place. We show the possibility of varying the cut-off of the instrument from 1 to 6 nm, a wider size range than the one usually covered by the PSM. We also present a new inlet system, which allows automated measurements of the background, minimizes the diffusion losses in the sampling line and is equipped with an electrostatic filter to remove ions. Finally, our view of the guidelines for optimal use of the Airmodus nCNC are provided.

Description: Known and unknown unknowns: the application of ensemble techniques to uncertainty estimation in satellite remote sensing data Atmospheric Measurement Techniques Discussions, 8, 8509-8562, 2015 Author(s): A. C. Povey and R. G. Grainger This paper discusses a best-practice representation of uncertainty in satellite remote sensing data. An estimate of uncertainty is necessary to make appropriate use of the information conveyed by a measurement. Traditional error propagation quantifies the uncertainty in a measurement due to well-understood perturbations in a measurement and auxiliary data – known, quantified "unknowns". The underconstrained nature of most satellite remote sensing observations requires the use of various approximations and assumptions that produce non-linear systematic errors that are not readily assessed – known, unquantifiable "unknowns". Additional errors result from the inability to resolve all scales of variation in the measured quantity – unknown "unknowns". The latter two categories of error are dominant in underconstrained remote sensing retrievals and the difficulty of their quantification limits the utility of existing uncertainty estimates, degrading confidence in such data. This paper proposes the use of ensemble techniques to present multiple self-consistent realisations of a data set as a means of depicting unquantified uncertainties. These are generated using various systems (different algorithms or forward models) believed to be appropriate to the conditions observed. Benefiting from the experience of the climate modelling community, an ensemble provides a user with a more complete representation of the uncertainty as understood by the data producer and greater freedom to consider different realisations of the data.

Description: Improved stratospheric aerosol extinction profiles from SCIAMACHY: validation and sample results Atmospheric Measurement Techniques Discussions, 8, 8353-8383, 2015 Author(s): C. von Savigny, F. Ernst, A. Rozanov, R. Hommel, K.-U. Eichmann, V. Rozanov, J. P. Burrows, and L. W. Thomason Stratospheric aerosol extinction profiles have been retrieved from SCIAMACHY/Envisat measurements of limb-scattered solar radiation. The retrieval is an improved version of an algorithm presented earlier. The retrieved aerosol extinction profiles are compared to co-located aerosol profile measurements with the SAGE II solar occultation instrument at a wavelength of 525 nm. Comparisons were carried out with two versions of the SAGE II data set (version 6.2 and the new version 7.0). In a global average sense the SCIAMACHY and the SAGE II version 7.0 extinction profiles agree to within about 10 % for altitudes above 15 km. Larger relative differences (up to 40 %) are observed at specific latitudes and altitudes. We also find differences between the two SAGE II data versions of up to 40 % for specific latitudes and altitudes. Sample results on the latitudinal and temporal variability of stratospheric aerosol extinction and optical depth during the SCIAMACHY mission period are presented. The results indicate that a series of volcanic eruptions is responsible for the increase in stratospheric aerosol optical depth from 2002 to 2012. Above about 28 km altitude volcanic eruptions are found to have negligible impact in the period 2002 to 2012.

Description: Characterization and source apportionment of organic aerosol using offline aerosol mass spectrometry Atmospheric Measurement Techniques Discussions, 8, 8599-8644, 2015 Author(s): K. R. Daellenbach, C. Bozzetti, A. Křepelová, F. Canonaco, R. Wolf, P. Zotter, P. Fermo, M. Crippa, J. G. Slowik, Y. Sosedova, Y. Zhang, R.-J. Huang, L. Poulain, S. Szidat, U. Baltensperger, A. S. H. Prévôt, and I. El Haddad Field deployments of the Aerodyne Aerosol Mass Spectrometer (AMS) have significantly advanced real-time measurements and source apportionment of non-refractory particulate matter. However, the cost and complex maintenance requirements of the AMS make impractical its deployment at sufficient sites to determine regional characteristics. Furthermore, the negligible transmission efficiency of the AMS inlet for supermicron particles significantly limits the characterization of their chemical nature and contributing sources. In this study, we utilize the AMS to characterize the water-soluble organic fingerprint of ambient particles collected onto conventional quartz filters, which are routinely sampled at many air quality sites. The method was applied to 256 particulate matter (PM) filter samples (PM 1 , PM 2.5 , PM 10 ) collected at 16 urban and rural sites during summer and winter. We show that the results obtained by the present technique compare well with those from co-located online measurements, e.g. AMS or Aerosol Chemical Speciation Monitor (ACSM). The bulk recoveries of organic aerosol (60–91 %) achieved using this technique, together with low detection limits (0.8 μg of organic aerosol on the analyzed filter fraction) allow its application to environmental samples. We will discuss the recovery variability of individual hydrocarbon, oxygen containing and other ions. The performance of such data in source apportionment is assessed in comparison to ACSM data. Recoveries of organic components related to different sources as traffic, wood burning and secondary organic aerosol are presented. This technique, while subjected to the limitations inherent to filter-based measurements (e.g. filter artifacts and limited time resolution) may be used to enhance the AMS capabilities in measuring size-fractionated, spatially-resolved long-term datasets.

Description: Metrology of ground-based satellite validation: co-location mismatch and smoothing issues of total ozone comparisons Atmospheric Measurement Techniques Discussions, 8, 8023-8082, 2015 Author(s): T. Verhoelst, J. Granville, F. Hendrick, U. Köhler, C. Lerot, J.-P. Pommereau, A. Redondas, M. Van Roozendael, and J.-C. Lambert Comparisons with ground-based correlative measurements constitute a key component in the validation of satellite data on atmospheric composition. The error budget of these comparisons contains not only the measurement uncertainties but also several terms related to differences in sampling and smoothing of the inhomogeneous and variable atmospheric field. A versatile system for Observing System Simulation Experiments (OSSEs), named OSSSMOSE, is used here to quantify these terms. Based on the application of pragmatic observation operators onto high-resolution atmospheric fields, it allows a simulation of each individual measurement, and consequently also of the differences to be expected from spatial and temporal field variations between both measurements making up a comparison pair. As a topical case study, the system is used to evaluate the error budget of total ozone column (TOC) comparisons between on the one hand GOME-type direct fitting (GODFITv3) satellite retrievals from GOME/ERS2, SCIAMACHY/Envisat, and GOME-2/MetOp-A, and on the other hand direct-sun and zenith-sky reference measurements such as from Dobsons, Brewers, and zenith scattered light (ZSL-)DOAS instruments respectively. In particular, the focus is placed on the GODFITv3 reprocessed GOME-2A data record vs. the ground-based instruments contributing to the Network for the Detection of Atmospheric Composition Change (NDACC). The simulations are found to reproduce the actual measurements almost to within the measurement uncertainties, confirming that the OSSE approach and its technical implementation are appropriate. This work reveals that many features of the comparison spread and median difference can be understood as due to metrological differences, even when using strict co-location criteria. In particular, sampling difference errors exceed measurement uncertainties regularly at most mid- and high-latitude stations, with values up to 10 % and more in extreme cases. Smoothing difference errors only play a role in the comparisons with ZSL-DOAS instruments at high latitudes, especially in the presence of a polar vortex. At tropical latitudes, where TOC variability is lower, both types of errors remain below about 1 % and consequently do not contribute significantly to the comparison error budget. The detailed analysis of the comparison results, including now the metrological errors, suggests that the published random measurement uncertainties for GODFITv3 reprocessed satellite data are potentially overestimated, and adjustments are proposed here. This successful application of the OSSSMOSE sytem to close for the first time the error budget of TOC comparisons, bodes well for potential future applications, which are briefly touched upon.

Description: Gas adsorption and desorption effects on cylinders and their importance for long-term gas records Atmospheric Measurement Techniques Discussions, 8, 8083-8112, 2015 Author(s): M. C. Leuenberger, M. F. Schibig, and P. Nyfeler It is well known that gases adsorb on many surfaces, in particular metal surfaces. There are two main forms responsible for these effects (i) physisorption and (ii) chemisorption. Physisorption is associated with lower binding energies in the order of 1–10 kJ mol −1 compared to chemisorption ranging from 100 to 1000 kJ mol −1 . Furthermore, chemisorption forms only monolayers, contrasting physisorption that can form multilayer adsorption. The reverse process is called desorption and follows similar mathematical laws, however, it can be influenced by hysteresis effects. In the present experiment we investigated the adsorption/desorption phenomena on three steel and three aluminium cylinders containing compressed air in our laboratory and under controlled conditions in a climate chamber, respectively. We proved the pressure effect on physisorption for CO 2 , CH 4 and H 2 O by decanting one steel and two aluminium cylinders completely. The CO 2 results for both cylinders are in excellent agreement with the pressure dependence of a monolayer adsorption model. However, adsorption on aluminium ( 〈 0.05 and 0 ppm for CO 2 and H 2 O) was about 10 times less than on steel ( 〈 0.41 ppm and about 〈 2.5 ppm, respectively). The CO 2 amounts adsorbed (5.8 × 10 19 CO 2 molecules) corresponds to about the five-fold monolayer adsorption indicating that the effective surface exposed for adsorption is significantly larger than the geometric surface area. Adsorption/desorption effects were minimal for CH 4 and for CO. However, the latter dependence requires further attention since it was only studied on one aluminium cylinder with a very low mole fraction. In the climate chamber the cylinders were exposed to temperatures between −10 and +50 °C to determine the corresponding temperature coefficients of adsorption. Again, we found distinctly different values for CO 2 ranging from 0.0014 to 0.0184 ppm °C −1 for steel cylinders and −0.0002 to −0.0003 ppm °C −1 for aluminium cylinders. The reversed temperature dependence for aluminium cylinders point to significantly lower desorption energies than for steel cylinders and might at least partly be due to temperature and gas consumption induced pressure changes. Temperature coefficients for CH 4 , CO and H 2 O adsorption were, within their error bands, insignificant. These results do indicate the need for careful selection and usage of gas cylinders for high precision calibration purposes such as requested in trace gas applications.

Description: A dual, single detector relaxed eddy accumulation system for long-term measurement of mercury flux Atmospheric Measurement Techniques Discussions, 8, 8113-8156, 2015 Author(s): S. Osterwalder, J. Fritsche, M. B. Nilsson, C. Alewell, J. Sommar, G. Jocher, M. Schmutz, J. Rinne, and K. Bishop The fate of anthropogenic emissions of mercury (Hg) to the atmosphere is influenced by the exchange of elemental Hg with the earth surface. This exchange which holds the key to a better understanding of Hg cycling from local to global scales has been difficult to quantify. To advance and facilitate research about land–atmosphere Hg interactions, we developed a dual-intake, single analyzer Relaxed Eddy Accumulation (REA) system. REA is an established technique for measuring turbulent fluxes of trace gases and aerosol particles in the atmospheric surface layer. Accurate determination of gaseous elemental mercury (GEM) fluxes has proven difficult to technical challenges presented by extremely small concentration differences (typically 〈 0.5 ng m −3 ) between updrafts and downdrafts. To address this we present an advanced REA design that uses two inlets and two pair of gold cartridges for semi-continuous monitoring of GEM fluxes. They are then analyzed sequentially on the same detector while another pair of gold cartridges takes over the sample collection. We also added a reference gas module for repeated quality-control measurements. To demonstrate the system performance, we present results from field campaigns in two contrasting environments: an urban setting with a heterogeneous fetch and a boreal mire during snow-melt. The observed emission rates were 15 and 3 ng m −2 h −1 . We claim that this dual-inlet, single detector approach is a significant development of the REA system for ultra-trace gases and can help to advance our understanding of long-term land–atmosphere GEM exchange.

Description: Sensitivity of remotely-sensed trace gas concentrations to polarisation Atmospheric Measurement Techniques Discussions, 8, 8779-8816, 2015 Author(s): D. M. O'Brien, I. N. Polonsky, and J. B. Kumer Current and proposed space missions estimate column-averaged concentrations of trace gases (CO 2 , CH 4 and CO) from high resolution spectra of reflected sunlight in absorption bands of the gases. The radiance leaving the top of the atmosphere is partially polarised by both reflection at the surface and scattering within the atmosphere. Generally the polarisation state is unknown, and could degrade the accuracy of the concentration measurements. The sensitivity to polarisation is modelled for the proposed geoCARB instrument, which will include neither polarisers nor polarisation scramblers to select particular polarisation states from the incident radiation. The radiometric and polarimetric calibrations proposed for geoCARB are outlined, and a model is developed for the polarisation properties of the geoCARB spectrographs. This model depends principally upon the efficiencies of the gratings to polarisations parallel and perpendicular to the rulings of the gratings. Next an ensemble of polarised spectra is simulated for geoCARB observing targets in India, China and Australia from geostationary orbit at longitude 110° E. The spectra are analysed to recover the trace gas concentrations in two modes, the first denied access to the polarimetric calibration and the second with access. The retrieved concentrations using the calibration data are almost identical to those that would be obtained with polarisation scramblers, while the retrievals without calibration data contain outliers that do not meet the accuracies demanded by the mission.

Description: Observations of XCO 2 and XCH 4 with ground-based high-resolution FTS at Saga, Japan and comparisons with GOSAT products Atmospheric Measurement Techniques Discussions, 8, 8257-8294, 2015 Author(s): H. Ohyama, S. Kawakami, T. Tanaka, I. Morino, O. Uchino, M. Inoue, T. Sakai, T. Nagai, A. Yamazaki, A. Uchiyama, T. Fukamachi, M. Sakashita, T. Kawasaki, T. Akaho, K. Arai, and H. Okumura Solar absorption spectra in the near-infrared region have been continuously acquired with a ground-based (g-b) high-resolution Fourier transform spectrometer (FTS) at Saga, Japan since July 2011. Column-averaged dry-air mole fractions of greenhouse gases were retrieved from the measured spectra for the period from July 2011 to December 2014. Aircraft measurements of CO 2 and CH 4 for calibrating the g-b FTS data were performed in January 2012 and 2013, and it is found that the g-b FTS and aircraft data agree to within ±0.2 %. The column-averaged dry-air mole fractions of CO 2 and CH 4 (XCO 2 and XCH 4 ) show increasing trends, with average growth rates of 2.3 ppm yr −1 and 9.5 ppb yr −1 , respectively, during the ~ 3.5 yr of observation. We compared the g-b FTS XCO 2 and XCH 4 data with those derived from backscattered solar spectra in the short-wavelength infrared region measured with Thermal And Near-infrared Sensor for carbon Observation-Fourier Transform Spectrometer (TANSO-FTS) onboard the Greenhouse gases Observing SATellite (GOSAT). Average differences between TANSO-FTS and g-b FTS data (TANSO-FTS minus g-b FTS) are 0.40 ± 2.51 ppm and −7.6 ± 13.7 ppb for XCO 2 and XCH 4 , respectively. Using aerosol information measured with a sky radiometer at Saga, we found that the differences between the TANSO-FTS and g-b FTS data are moderately negatively correlated with aerosol optical thickness and do not depend explicitly on aerosol size. In addition, from aerosol profiles measured with lidar located right by the g-b FTS, we were able to show that cirrus clouds and tropospheric aerosols accumulated in the lower layers of the atmosphere tend to overestimate or underestimate the TANSO-FTS data.

Description: New image measurements of the gravity wave propagation characteristics from a low latitude Indian station Atmospheric Measurement Techniques Discussions, 8, 8231-8255, 2015 Author(s): M. Sivakandan, A. Taori, and K. Niranjan The image observations of mesospheric O( 1 S) 558 nm have been performed from a low latitude Indian station, Gadanki (13.5° N; 79.2° E) using a CCD based all sky camera system. Based on three years (from year 2012 to the year 2014) of image data during March–April, we characterize the small scale gravity wave properties. We noted 50 strong gravity wave event and 19 ripple events to occur. The horizontal wavelengths of the gravity waves are found to vary from 12 to 42 km with the phase velocity ranging from 20 to 90 km. In most cases, these waves were propagating towards north with only a few occasions of southward propagation. The outgoing longwave radiation data suggest that lower atmospheric convection was most possible reason for the generation of the waves observed in the airglow data.

Description: Retrieval algorithm for rainfall mapping from microwave links in a cellular communication network Atmospheric Measurement Techniques Discussions, 8, 8191-8230, 2015 Author(s): A. Overeem, H. Leijnse, and R. Uijlenhoet Microwave links in commercial cellular communication networks hold a promise for areal rainfall monitoring and could complement rainfall estimates from ground-based weather radars, rain gauges, and satellites. It has been shown that country-wide rainfall maps can be derived from the signal attenuations of microwave links in such a network. Here we give a detailed description of the employed rainfall retrieval algorithm and provide the corresponding code. Moreover, the code (in the scripting language "R") is made available including a data set of commercial microwave links. The purpose of this paper is to promote rainfall monitoring utilizing microwave links from cellular communication networks as an alternative or complementary means for global, continental-scale rainfall monitoring.

Description: Assessment of adequate quality and collocation of reference measurements with space borne hyperspectral infrared instruments to validate retrievals of temperature and water vapour Atmospheric Measurement Techniques Discussions, 8, 5591-5614, 2015 Author(s): X. Calbet A method is presented to assess whether a given reference ground based point observation, typically a radiosonde measurement, is adequately collocated and sufficiently representative of space borne hyperspectral infrared instrument measurements. Once this assessment is made, the ground based data can be used to validate and potentially calibrate, with a high degree of accuracy, the hyperspectral retrievals of temperature and water vapour.

Description: H 2 S interference on CO 2 isotopic measurements using a Picarro G1101-i cavity ring-down spectrometer Atmospheric Measurement Techniques Discussions, 8, 5651-5675, 2015 Author(s): K. Malowany, J. Stix, A. Van Pelt, and G. Lucic Cavity ring-down spectrometers (CRDS) have the capacity to make isotopic measurements of CO 2 where concentrations range from atmospheric (~ 400 ppm) to 6000 ppm. Following field trials, it has come to light that the spectrographic lines used for CO 2 have an interference with elevated (higher than ambient) amounts of hydrogen sulfide (H 2 S), which causes significant depletions in the δ 13 C measurement by the CRDS. In order to deploy this instrument in environments with elevated H 2 S concentrations (i.e., active volcanoes), we require a robust method for eliminating this interference. Controlled experiments using a Picarro G1101-i optical spectrometer were done to characterize the H 2 S interference at varying CO 2 and H 2 S concentrations. The addition of H 2 S to a CO 2 standard gas reveals an increase in the 12 CO 2 concentration and a more significant decrease in the 13 CO 2 concentration, resulting in a depleted δ 13 C value. Reacting gas samples containing H 2 S with copper prior to analysis can eliminate this effect. However, experiments also revealed that the addition of H 2 S to CO 2 results in the formation of carbonyl sulfide (OCS) and carbon disulfide (CS 2 ), causing a decrease in the overall CO 2 concentration without affecting the δ 13 C value. It is important for future work with CRDS, particularly in volcanic regions where H 2 S is abundant, to be aware of the H 2 S interference on the CO 2 spectroscopic lines and to remove all H 2 S prior to analysis. We suggest employing a scrub composed of copper to remove H 2 S from all gas samples that have concentrations in excess of 1 ppb.

Description: Long-term variability of aerosol optical thickness in Eastern Europe over 2001–2014 according to the measurements at the Moscow MSU MO AERONET site with additional cloud and NO 2 correction Atmospheric Measurement Techniques Discussions, 8, 7843-7878, 2015 Author(s): N. Y. Chubarova, A. A. Poliukhov, and I. D. Gorlova The aerosol properties of the atmosphere were obtained within the framework of the AERONET program at the Moscow State University Meteorological Observatory (Moscow MSU MO) over 2001–2014 period. The quality data control has revealed the necessity of their additional cloud and NO 2 correction. The application of cloud correction according to hourly visual cloud observations provides a decrease in average aerosol optical thickness (AOT) at 500 nm of up to 0.03 compared with the standard dataset. We also show that the additional NO 2 correction of the AERONET data is needed in large megalopolis, like Moscow, with 12 million residents and the NO x emission rates of about 100 kt yr −1 . According to the developed method we estimated monthly mean NO 2 content, which provides an additional decrease of 0.01 for AOT at 340 nm, and of about 0.015 – for AOT at 380 and 440 nm. The ratios of NO 2 optical thickness to AOT at 380 and 440 nm are about 5–6 % in summer and reach 15–20 % in winter when both factors have similar effects on UV irradiance. Seasonal cycle of AOT at 500 nm is characterized by a noticeable summer and spring maxima, and minimum in winter conditions, changing from 0.08 in December and January up to 0.3 in August. The application of the additional cloud correction removes a local AOT maximum in February, and lowered the December artificial high AOT values. The pronounced negative AOT trends of about −1–5 % yr −1 have been obtained for most months, which could be attributed to the negative trends in emissions ( E ) of different aerosol precursors of about 116 Gg yr −2 in E SO x , 78 Gg yr −2 in E NMVOC , and 272 Gg yr −2 in E CO over European territory of Russia. No influence of natural factors on temporal AOT variations has been revealed.

Description: The GOME-2 instrument on the Metop series of satellites: instrument design, calibration, and level 1 data processing – an overview Atmospheric Measurement Techniques Discussions, 8, 8645-8700, 2015 Author(s): R. Munro, R. Lang, D. Klaes, G. Poli, C. Retscher, R. Lindstrot, R. Huckle, A. Lacan, M. Grzegorski, A. Holdak, A. Kokhanovsky, J. Livschitz, and M. Eisinger The Global Ozone Monitoring Experiment-2 (GOME-2) flies on the Metop series of satellites, the space component of the EUMETSAT Polar System. In this paper we will provide an overview of the instrument design, the on-ground calibration and characterisation activities, in-flight calibration, and level 0 to 1 data processing. The quality of the level 1 data is presented and points of specific relevance to users are highlighted. Long-term level 1 data consistency is also discussed and plans for future work are outlined. The information contained in this paper summarises a large number of technical reports and related documents containing information that is not currently available in the published literature. These reports and documents are however made available on the EUMETSAT web pages ( http://www.eumetsat.int ) and readers requiring more details than can be provided in this overview paper will find appropriate references at relevant points in the text.

Description: Dual-wavelength light scattering for selective detection of volcanic ash particles Atmospheric Measurement Techniques Discussions, 8, 8701-8726, 2015 Author(s): Z. Jurányi, H. Burtscher, M. Loepfe, M. Nenkov, and E. Weingartner A new method is presented in this paper which analyses the scattered light of individual aerosol particles simultaneously at two different wavelengths in order to retrieve information on the particle type. We show that dust-like particles, such as volcanic ash, can be unambiguously discriminated from water droplets on a single particle level. As a future application of this method, the detection of volcanic ash particles should be possible in a humid atmosphere in the presence of cloud droplets. We show an example, how the characteristic behaviour of pure water's refractive index can be used to separate water droplets and dust-like particles which are commonly found in the micrometer size-range in the ambient air. The low real part of the water's refractive index around 2700–2800 nm results in low scattered light intensities compared to e.g. the visible wavelength range and this feature can be used for the particle identification. The two-wavelength measurement setup was theoretically and experimentally tested and studied. Theoretical calculations were done using Mie theory. Comparing the ratio of the scattered light at the two wavelengths ( R value) for water droplets and different dust types (basalt, andesite, African mineral dust, sand, volcanic ash, pumice) showed at least 9 times higher values (on average 70 times) for water droplets than for the dust types at any diameter within the particle size range of 2–20 μm . The envisaged measurement setup was built up into a laboratory prototype and was tested with different types of aerosols. We generated aerosols from the following powders simulating dust-like particles: cement dust, ISO 12103-1 A1 Ultrafine Test Dust and Ash from the 2012 eruption of the Etna volcano. Our measurements verified the theoretical considerations, the median experimental R value is 8–21 times higher for water than for the "dust" particles.

Description: Measurement of wind profiles by motion-stabilised ship-borne Doppler lidar Atmospheric Measurement Techniques Discussions, 8, 9339-9372, 2015 Author(s): P. Achtert, I. M. Brooks, B. J. Brooks, B. I. Moat, J. Prytherch, P. O. G. Persson, and M. Tjernström Three months of Doppler lidar wind measurements were obtained during the Arctic Cloud Summer Experiment on the icebreaker Oden during the summer of 2014. Such ship-borne measurements require active stabilisation to remove the effects of ship motion. We demonstrate that the combination of a commercial Doppler lidar with a custom-made motion-stabilisation platform enables the retrieval of wind profiles in the Arctic boundary layer during both cruising and ice-breaking with statistical uncertainties comparable to land-based measurements. This holds particularly within the planetary boundary layer even though the overall aerosol load was very low. Motion stabilisation was successful for high wind speeds in open water and the resulting wave conditions. It allows for the retrieval of winds with a random error below 0.2 m s −1 , comparable to the measurement error of standard radiosondes. The combination of a motion-stabilised platform with a low-maintenance autonomous Doppler lidar has the potential to enable continuous long-term high-resolution ship-based wind profile measurements over the oceans.

Description: Thermal-optical analysis for the measurement of elemental carbon (EC) and organic carbon (OC) in ambient air a literature review Atmospheric Measurement Techniques Discussions, 8, 9649-9712, 2015 Author(s): A. Karanasiou, M. C. Minguillón, M. Viana, A. Alastuey, J.-P. Putaud, W. Maenhaut, P. Panteliadis, G. Močnik, O. Favez, and T. A. J. Kuhlbusch Thermal-optical analysis is currently under consideration by the European standardization body (CEN) as the reference method to quantitatively determine organic carbon (OC) and elemental carbon (EC) in ambient air. This paper presents an overview of the critical parameters related to the thermal-optical analysis including thermal protocols, critical factors and interferences of the methods examined, method inter-comparisons, inter-laboratory exercises, biases and artifacts, and reference materials. The most commonly used thermal protocols include NIOSH-like, IMPROVE_A and EUSAAR_2 protocols either with light transmittance or reflectance correction for charring. All thermal evolution protocols are comparable for total carbon (TC) concentrations but the results vary significantly concerning OC and especially EC concentrations. Thermal protocols with a rather low peak temperature in the inert mode like IMPROVE_A and EUSAAR_2 tend to classify more carbon as EC compared to NIOSH-like protocols, while charring correction based on transmittance usually leads to smaller EC values compared to reflectance. The difference between reflectance and transmittance correction tends to be larger than the difference between different thermal protocols. Nevertheless, thermal protocols seem to correlate better when reflectance is used as charring correction method. The difference between EC values as determined by the different protocols is not only dependent on the optical pyrolysis correction method, but also on the chemical properties of the samples due to different contributions from various sources. The overall conclusion from this literature review is that it is not possible to identify the "best" thermal-optical protocol based on literature data only, although differences attributed to the methods have been quantified when possible.

Description: Measurement of aerosol optical depth and sub-visual cloud detection using the optical depth sensor (ODS) Atmospheric Measurement Techniques Discussions, 8, 9611-9648, 2015 Author(s): D. Toledo, P. Rannou, J.-P. Pommereau, A. Sarkissian, and T. Foujols A small and sophisticated optical depth sensor (ODS) has been designed to work in the atmosphere of Earth and Mars. The instrument measures alternatively the diffuse radiation from the sky and the attenuated direct radiation from the sun on the surface. The principal goals of ODS are to retrieve the daily mean aerosol optical depth (AOD) and to detect very high and optically thin clouds, crucial parameters in understanding the Martian and Earth meteorology and climatology. The detection of clouds is undertaken at twilight, allowing the detection and characterization of clouds with opacities below 0.03 (sub-visual clouds). In addition, ODS is capable to retrieve the aerosol optical depth during night-time from moonlight measurements. In order to study the performance of ODS under Mars-like conditions as well as to evaluate the retrieval algorithms for terrestrial measurements, ODS was deployed in Ouagadougou (Africa) between November 2004 and October 2005, a sahelian region characterized by its high dust aerosol load and the frequent occurrence of Saharan dust storms. The daily average AOD values retrieved by ODS were compared with those provided by a CIMEL Sun-photometer of the AERONET (Aerosol Robotic NETwork) network localized at the same location. Results represent a good agreement between both ground-based instruments, with a correlation coefficient of 0.79 for the whole data set and 0.96 considering only the cloud-free days. From the whole dataset, a total of 71 sub-visual cirrus (SVC) were detected at twilight with opacities as thin as 1.10 −3 and with a maximum of occurrence at altitudes between 14 and 20 km. Although further analysis and comparisons are required, results indicate the potential of ODS measurements to detect sub-visual clouds.

Description: A broad supersaturation scanning (BS2) approach for rapid measurement of aerosol particle hygroscopicity and cloud condensation nuclei activity Atmospheric Measurement Techniques Discussions, 8, 9713-9730, 2015 Author(s): H. Su, Y. Cheng, N. Ma, Z. Wang, X. Wang, M. Pöhlker, B. Nillius, A. Wiedensohler, and U. Pöschl The activation and hygroscopicity of cloud condensation nuclei (CCN) are key to understand aerosol–cloud interactions and their climate impact. It can be measured by scanning the particle size and supersaturation in CCN measurements. The scanning of supersaturation is often time-consuming and limits the temporal resolution and performance of CCN measurements. Here we present a new approach, termed broad supersaturation scanning (BS2) method, in which a range of supersaturation is simultaneously scanned reducing the time interval between different supersaturation scans. The practical applicability of the BS2 approach is demonstrated with nano-CCN measurements of laboratory-generated aerosol particles. Model simulations show that the BS2 approach is also applicable for measuring CCN activation of ambient mixed particles. Due to its fast response and technical simplicity, the BS2 approach may be well suited for long-term measurements. Since hygroscopicity is closely related to the fraction of organics/inorganics in aerosol particles, a BS2-CCN counter can also serve as a complementary sensor for fast detection/estimation of aerosol chemical compositions.

Description: Carbon monoxide total columns from SCIAMACHY 2.3 μm atmospheric reflectance measurements: towards a full-mission data product (2003–2012) Atmospheric Measurement Techniques Discussions, 8, 9731-9783, 2015 Author(s): T. Borsdorff, P. Tol, J. E. Williams, J. de Laat, J. aan de Brugh, P. Nédélec, I. Aben, and J. Landgraf We present a full-mission data product of carbon monoxide (CO) vertical column densities using the 2310–2338 nm SCIAMACHY reflectance measurements over clear sky land scenes for the period January 2003–April 2012. The retrieval employs the SICOR algorithm, which will be used for operational data processing of the Sentinel-5 Precursor mission, combined with a SCIAMACHY specific radiometric soft-calibration to mitigate instrumental issues. The retrieval approach infers simultaneously carbon monoxide, methane and water vapour column densities together with a Lambertian surface albedo from individual SCIAMACHY measurements employing a non-scattering radiative transfer model. To account for the radiometric instrument degradation including the formation of an ice-layer on the 2.3 μm detector-array, we consider clear sky measurements over the Sahara as a natural calibration target. For these specific measurements, we spectrally calibrate the SCIAMACHY measurements and determine a spectral radiometric offset and the width of the instrument spectral response function as a function of time for the entire operational phase of the mission. We show that the smoothing error of individual clear sky CO retrievals is less than ±1 ppb and thus this error contribution has not to be accounted for in the validation considering the much higher retrieval noise. The CO data product is validated against measurements of ground-based Fourier transform infrared spectrometers at 27 stations of the NDACC-IRWG and TCCON network and MOZAIC/IAGOS aircraft measurements at 26 airports worldwide. Overall, we find a good agreement with TCCON measurements with a mean bias b = −1.2 ppb and a station-to-station bias with σ = 7.2 ppb. For the NDACC-IRWG network, we obtain a larger mean station bias of b = −9.2 ppb with σ = 8.1 ppb and for the MOZAIC/IAGOS measurements we find b = −6.4 ppb with σ = 5.6 ppb. The SCIAMACHY data set is subject to a small but significant trend of 1.47 ± 0.25 ppb yr −1 . After trend correction, the bias with respect to MOZAIC/IAGOS observation is 2.5 ppb, with respect to TCCON measurements it is −4.6 ppb and with respect to NDACC-IRWG measurements −8.4 ppb. Hence, a discrepancy of 3.8 ppb remains between the global biases with NDACC-IRWG and TCCON, which is confirmed by directly comparing NDACC-IRWG and TCCON measurements. Generally, the scatter of the individual SCIAMACHY CO retrievals is high and dominated by large measurement noise. Hence, for practical usage of the dataset, averaging of individual retrievals is required. As an example, we show that monthly mean SCIAMACHY CO retrievals, averaged separately over Northern and Southern Africa, reflect the spatial and temporal variability of biomass burning events in agreement with the global chemical transport model TM5.

Description: Ionosonde measurements in Bayesian statistical ionospheric tomography with incoherent scatter radar validation Atmospheric Measurement Techniques Discussions, 8, 9823-9851, 2015 Author(s): J. Norberg, I. I. Virtanen, L. Roininen, J. Vierinen, M. Orispää, K. Kauristie, and M. S. Lehtinen We validate two-dimensional ionospheric tomography reconstructions against EISCAT incoherent scatter radar measurements. Our tomography method is based on Bayesian statistical inversion with prior distribution given by its mean and covariance. We employ ionosonde measurements for the choice of the prior mean and covariance parameters, and use the Gaussian Markov random fields as a sparse matrix approximation for the numerical computations. This results in a computationally efficient and statistically clear inversion algorithm for tomography. We demonstrate how this method works with simultaneous beacon satellite and ionosonde measurements obtained in northern Scandinavia. The performance is compared with results obtained with a zero mean prior and with the prior mean taken from the International Reference Ionosphere 2007 model. In validating the results, we use EISCAT UHF incoherent scatter radar measurements as the ground truth for the ionization profile shape. We find that ionosonde measurements improve the reconstruction by adding accurate information about the absolute value and the height distribution of electron density, and outperforms the alternative prior information sources. With an ionosonde at continuous disposal, the presented method enhances stand-alone near real-time ionospheric tomography for the given conditions significantly.

Description: A microwave satellite water vapour column retrieval for polar winter conditions Atmospheric Measurement Techniques Discussions, 8, 9959-9992, 2015 Author(s): C. Perro, G. Lesins, T. Duck, and M. Cadeddu A new microwave satellite water vapour retrieval for use in polar winter conditions is presented. The retrieval employs a priori information and an iterative approach. It is tested using simulated and actual measurements from the Microwave Humidity Sounder (MHS) satellite instruments. Ground truth is provided by the G-band vapor radiometer (GVR) at Barrow, Alaska. For water vapour columns less than 6 kg m −2 , comparison with the GVR gives a standard deviation of 0.39 kg m −2 and a systematic bias of 0.08 kg m −2 . The errors are shown to be significantly less than for other satellite measurement systems. The errors are comparable to those from atmospheric reanalyses; however, the MHS data come at much higher horizontal resolution ( 〈 40 km) and are shown to reveal more structure. The retrieval can be used to obtain pan-Arctic maps of water vapour columns of unprecedented quality. The retrieval may also be applied to the Special Sensor Microwave Imager/Sounder (SSMIS) and the Advanced Technology Microwave Sounder (ATMS).

Description: Broadband cavity enhanced spectroscopy in the ultraviolet spectral region for measurements of nitrogen dioxide and formaldehyde Atmospheric Measurement Techniques Discussions, 8, 9927-9958, 2015 Author(s): R. A. Washenfelder, A. R. Attwood, J. M. Flores, Y. Rudich, and S. S. Brown Formaldehyde (CH 2 O) is the most abundant aldehyde in the atmosphere, and strongly affects photochemistry through its photolysis. We describe simultaneous measurements of CH 2 O and nitrogen dioxide (NO 2 ) using broadband cavity enhanced spectroscopy in the ultraviolet spectral region. The light source consists of a continuous-wave diode laser focused into a Xenon bulb to produce a plasma that emits high-intensity, broadband light. The plasma discharge is optically filtered and coupled into a 1 m optical cavity. The reflectivity of the cavity mirrors is 0.99933 ± 0.00003 (670 ppm loss) at 338 nm, as determined from the known Rayleigh scattering of He and zero air. This mirror reflectivity corresponds to an effective path length of 1.49 km within the 1 m cell. We measure the cavity output over the 315–350 nm spectral region using a grating monochromator and charge-coupled device (CCD) array detector. We use published reference spectra with spectral fitting software to simultaneously retrieve CH 2 O and NO 2 concentrations. Independent measurements of NO 2 standard additions by broadband cavity enhanced spectroscopy and cavity ringdown spectroscopy agree within 2 % (slope for linear fit = 0.98 ± 0.03 with r 2 = 0.998). Standard additions of CH 2 O measured by broadband cavity enhanced spectroscopy and calculated based on flow dilution are also well-correlated, with r 2 = 0.9998. During constant, mixed additions of NO 2 and CH 2 O, the 30 s measurement precisions (1 σ ) of the current configuration were 140 and 210 pptv, respectively. The current 1-min detection limit for extinction measurements at 315–350 nm provides sufficient sensitivity for measurement of trace gases in laboratory experiments and ground-based field experiments. Additionally, the instrument provides highly accurate, spectroscopically-based trace gas detection that may complement higher precision techniques based on non-absolute detection methods. In addition to trace gases, this approach will be appropriate for measurements of aerosol extinction in ambient air, and this spectral region is important for characterizing the strong ultraviolet absorption by brown carbon aerosol.

Description: Real time data acquisition of commercial microwave link networks for hydrometeorological applications Atmospheric Measurement Techniques Discussions, 8, 12243-12262, 2015 Author(s): C. Chwala, F. Keis, and H. Kunstmann The usage of data from commercial microwave link (CML) networks for scientific purposes is becoming increasingly popular, in particular for rain rate estimation. However, data acquisition and availability is still a crucial problem and limits research possibilities. To overcome this issue, we have developed an open source data acquisition system based on the Simple Network Management Protocol (SNMP). It is able to record transmitted- and received signal levels of a large number of CMLs simultaneously with a temporal resolution of up to one second. We operate this system at Ericsson Germany, acquiring data from 450 CMLs with minutely real time transfer to our data base. Our data acquisition system is not limited to a particular CML hardware model or manufacturer, though. We demonstrate this by running the same system for CMLs of a different manufacturer, operated by an alpine skiing resort in Germany. There, the data acquisition is running simultaneously for four CMLs with a temporal resolution of one second. We present an overview of our system, describe the details of the necessary SNMP requests and show results from its operational application.

Description: Evaluation of three lidar scanning strategies for turbulence measurements Atmospheric Measurement Techniques Discussions, 8, 12329-12381, 2015 Author(s): J. F. Newman, P. M. Klein, S. Wharton, A. Sathe, T. A. Bonin, P. B. Chilson, and A. Muschinski Several errors occur when a traditional Doppler-beam swinging (DBS) or velocity–azimuth display (VAD) strategy is used to measure turbulence with a lidar. To mitigate some of these errors, a scanning strategy was recently developed which employs six beam positions to independently estimate the u , v , and w velocity variances and covariances. In order to assess the ability of these different scanning techniques to measure turbulence, a Halo scanning lidar, WindCube v2 pulsed lidar and ZephIR continuous wave lidar were deployed at field sites in Oklahoma and Colorado with collocated sonic anemometers. Results indicate that the six-beam strategy mitigates some of the errors caused by VAD and DBS scans, but the strategy is strongly affected by errors in the variance measured at the different beam positions. The ZephIR and WindCube lidars overestimated horizontal variance values by over 60 % under unstable conditions as a result of variance contamination, where additional variance components contaminate the true value of the variance. A correction method was developed for the WindCube lidar that uses variance calculated from the vertical beam position to reduce variance contamination in the u and v variance components. The correction method reduced WindCube variance estimates by over 20 % at both the Oklahoma and Colorado sites under unstable conditions, when variance contamination is largest. This correction method can be easily applied to other lidars that contain a vertical beam position and is a promising method for accurately estimating turbulence with commercially available lidars.

Description: Predicting ambient aerosol thermal-optical reflectance (TOR) measurements from infrared spectra: extending the predictions to different years and different sites Atmospheric Measurement Techniques Discussions, 8, 12433-12474, 2015 Author(s): M. Reggente, A. M. Dillner, and S. Takahama Organic carbon (OC) and elemental carbon (EC) are major components of atmospheric particulate matter (PM), which has been associated with increased morbidity and mortality, climate change and reduced visibility. Typically OC and EC concentrations are measured using thermal optical methods such as thermal optical reflectance (TOR) from samples collected on quartz filters. In this work, we estimate TOR OC and EC using Fourier transform infrared (FT-IR) absorbance spectra from polytetrafluoroethylene (PTFE or Teflon) filters using partial least square regression (PLSR) calibrated to TOR OC and EC measurements for a wide range of samples. The proposed method can be integrated with analysis of routinely collected PTFE filter samples that, in addition to OC and EC concentrations, can concurrently provide information regarding the composition of the organic aerosol. We have used the FT-IR absorbance spectra and TOR OC and EC concentrations collected in the Interagency Monitoring of PROtected Visual Environment (IMPROVE) network (USA). We used 526 samples collected in 2011 at seven sites to calibrate the models, and more than 2000 samples collected in 2013 at 17 sites to test the models. Samples from six sites are present both in the calibration and test sets. The calibrations produce accurate predictions both for samples collected at the same six sites present in the calibration set ( R 2 =0.97 and R 2 =0.95 for OC and EC respectively), and for samples from nine of the 11 sites not included in the calibration set ( R 2 =0.96 and R 2 =0.91 for OC and EC respectively). Samples collected at the other two sites require a different calibration model to achieve accurate predictions. We also propose a method to anticipate the prediction error: we calculate the squared Mahalanobis distance in the feature space (scores determined by PLSR) between new spectra and spectra in the calibration set. The squared Mahalanobis distance provides a crude method for assessing the magnitude of mean error when applying a calibration model to a new set of samples.

Description: Improvement of the retrieval used for Karlsruhe TCCON data Atmospheric Measurement Techniques Discussions, 8, 12203-12242, 2015 Author(s): M. Kiel, D. Wunch, P. O. Wennberg, G. C. Toon, F. Hase, and T. Blumenstock We present a modified retrieval strategy for solar absorption spectra recorded by the Karlsruhe Fourier Transform Infrared (FTIR) spectrometer which is operational within the Total Carbon Column Observing Network (TCCON). In typical TCCON stations, the (3800–11 000) cm −1 spectral region is measured on a single extended Indium Gallium Arsenide (InGaAs) detector. The Karlsruhe setup instead splits the spectrum across an Indium Antimonide (InSb) and InGaAs detector through the use of a dichroic beam splitter. This permits measurements further into the mid infrared (MIR) that are of scientific interest, but are not considered TCCON measurements. This optical setup induces, however, larger variations in the continuum level of the solar spectra than the typical TCCON setup. Here we investigate the appropriate treatment of continuum level variations in the retrieval strategy using the spectra recorded in Karlsruhe. The broad spectral windows used by TCCON require special attention with respect to residual curvature in the spectral fits. To accommodate the unique setup of Karlsruhe, higher order discrete Legendre polynomial basis functions have been enabled in the TCCON retrieval code to fit the continuum. This improves spectral fits and airmass dependencies for affected spectral windows. After fitting the continuum curvature, the Karlsruhe greenhouse gas records are in good agreement with other European TCCON datasets. A new version (R1) of the Karlsruhe data using the modified retrieval strategy is available through CDIAC ( http://tccon.ornl.gov ). Future scientific studies should use this superior R1 data, instead of the obsolete R0 data.

Description: Validation of revised methane and nitrous oxide profiles from MIPAS-ENVISAT Atmospheric Measurement Techniques Discussions, 8, 12105-12153, 2015 Author(s): J. Plieninger, A. Laeng, S. Lossow, T. von Clarmann, G. P. Stiller, S. Kellmann, A. Linden, M. Kiefer, K. A. Walker, S. Noël, M. Hervig, M. McHugh, A. Lambert, J. Urban, J. W. Elkins, and D. Murtagh Improved versions of CH 4 and N 2 O profiles derived at the Institute of Meteorology and Climate Research and Instituto de Astrofísica de Andalucía (CSIC) from spectra measured by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) have become available. For the MIPAS full resolution period (2002–2004) these are V5H_CH4_21 and V5H_N2O_21 and for the reduced resolution period (2005–2012) these are V5R_CH4_224, V5R_CH4_225, V5R_N2O_224 and V5R_N2O_225. Here, we compare CH 4 profiles to those measured by the Fourier Transform Spectrometer on board of the Atmospheric Chemistry Experiment (ACE-FTS), the HALogen Occultation Experiment (HALOE) and the Scanning Imaging Absorption Spectrometer for Atmospheric CHartographY (SCIAMACHY) and to the Global Cooperative Air Sampling Network (GCASN) surface data. We find the MIPAS CH 4 profiles below 25 km to be typically higher in the order of 0.1 ppmv for both measurement periods. N 2 O profiles are compared to those measured by ACE-FTS, the Microwave Limb Sounder on board of the Aura satellite (Aura-MLS) and the Sub-millimetre Radiometer on board of the Odin satellite (Odin-SMR) as well as to the Halocarbons and other Atmospheric Trace Species Group (HATS) surface data. The mixing ratios from the satellite instruments agree well for the full resolution period. For the reduced resolution period, MIPAS produces similar values as Odin-SMR, but higher values than ACE-FTS and HATS. Below 27 km, the MIPAS profiles show higher mixing ratios than Aura-MLS, and lower values between 27 and 41 km. Cross comparisons between the two MIPAS measurement periods show that they generally agree quite well, but, especially for CH 4 , the reduced resolution period seems to produce slightly higher mixing ratios than the full resolution data.

Description: GFIT2: an experimental algorithm for vertical profile retrieval from near IR spectra Atmospheric Measurement Techniques Discussions, 8, 12263-12295, 2015 Author(s): B. J. Connor, V. Sherlock, G. Toon, D. Wunch, and P. Wennberg An algorithm for retrieval of vertical profiles from ground-based spectra in the near IR is described and tested. Known as GFIT2, the algorithm is primarily intended for CO 2 , and is used exclusively for CO 2 in this paper. Retrieval of CO 2 vertical profiles from ground-based spectra is theoretically possible, would be very beneficial for carbon cycle studies and the validation of satellite measurements, and has been the focus of much research in recent years. GFIT2 is tested by application both to synthetic spectra, and to measurements at two TCCON sites. We demonstrate that there are approximately 3° of freedom for the CO 2 profile, and the algorithm performs as expected on synthetic spectra. We show that the accuracy of retrievals of CO 2 from measurements in the 1.6 μ spectral band is limited by small uncertainties in calculation of the atmospheric spectrum. We investigate several techniques to minimize the effect of these uncertainties in calculation of the spectrum. These techniques are somewhat effective, but to date have not been demonstrated to produce CO 2 profile retrievals superior to existing techniques for retrieval of column abundance. We finish by discussing on-going research which may allow CO 2 profile retrievals with sufficient accuracy to significantly improve on the results of column retrievals, both in total column abundance and in profile shape.

Description: The detection of carbon dioxide leaks using quasi-tomographic laser absorption spectroscopy measurements in variable wind Atmospheric Measurement Techniques Discussions, 8, 12297-12327, 2015 Author(s): Z. H. Levine, A. L. Pintar, J. Dobler, N. Blume, M. Braun, T. S. Zaccheo, and T. G. Pernini Laser Absorption Spectroscopy (LAS) has been used over the last several decades for the measurement of trace gasses in the atmosphere. For over a decade, LAS measurements from multiple sources and tens of retroreflectors have been combined with sparse-sample tomography methods to estimate the 2-D distribution of trace gas concentrations and underlying fluxes from pointlike sources. In this work, we consider the ability of such a system to detect and estimate the position and rate of a single point leak which may arise as a failure mode for carbon dioxide storage. The leak is assumed to be at a constant rate giving rise to a plume with a concentration and distribution that depend on the wind velocity. We demonstrate the ability of our approach to detect a leak using numerical simulation and a preliminary measurement.

Description: Twin-cuvette measurement technique for investigation of dry deposition of O 3 and PAN to plant leaves under controlled humidity conditions Atmospheric Measurement Techniques Discussions, 8, 12051-12104, 2015 Author(s): S. Sun, A. Moravek, L. von der Heyden, A. Held, M. Sörgel, and J. Kesselmeier We present a dynamic twin-cuvette system for quantifying the trace gas exchange fluxes between plants and the atmosphere under controlled temperature, light and humidity conditions. Compared with a single cuvette system, the twin-cuvette system is insensitive for disturbing background effects such as wall deposition. In combination with a climate chamber we can perform flux measurements under constant and controllable environmental conditions. With an Automatic Temperature Regulated Air Humidification System (ATRAHS) we are able to regulate the relative humidity inside both cuvettes between 40 to 90 % with a high precision of 0.3 %. Thus, we could demonstrate that for a cuvette system operated with a high flow rate (〉 20 L min −1 ) such a temperature regulated humidification system as ATRAHS is an accurate method for air humidification of the flushing air. Furthermore, the fully automatic progressive fill-up of ATRAHS based on a floating valve improved the performance of the entire measurement system and prevented data gaps. Two reactive gas species, ozone (O 3 ) and peroxyacetyl nitrate (PAN), were used to demonstrate the quality and performance of the twin-cuvette system. O 3 and PAN exchange with Quercus ilex was investigated over a 14 day measurement period under controlled climate chamber conditions. By using O 3 mixing ratios between 32–105 ppb and PAN mixing ratios between 100–350 ppt a linear dependency of the O 3 flux as well as the PAN flux in relation to its ambient mixing ratio could be observed. At relative humidity (RH) of 40 %, the deposition velocity ratio of O 3 and PAN was determined to be 0.45. At that humidity, the deposition of O 3 to the plant leaves was found to be only controlled by the leaf stomata. For PAN an additional resistance inhibited the uptake of PAN by the leaves. Furthermore, the formation of water films on the leaf surface of plants inside the chamber could be continuously tracked with our custom built leaf wetness sensors. Using this modified leaf wetness sensor measuring the electrical surface conductance on the leaves, an exponential relationship between the ambient humidity and the electrical surface conductance could be determined.

Description: Detection of ground fog in mountainous areas from MODIS day-time data using a statistical approach Atmospheric Measurement Techniques Discussions, 8, 12155-12201, 2015 Author(s): H. M. Schulz, B. Thies, S.-C. Chang, and J. Bendix The mountain cloud forest of Taiwan can be delimited from other forest types using a map of the ground fog frequency. In order to create such a frequency map from remotely sensed data, an algorithm able to detect ground fog is necessary. Common techniques for ground fog detection based on weather satellite data can not be applied to fog occurrences in Taiwan as they rely on several assumptions regarding cloud properties. Therefore a new statistical method for the detection of ground fog from MODIS data in mountainous terrain is presented. Due to the sharpening of input data using MODIS bands 1 and 2 the method provides fog masks in a resolution of 250 m per pixel. The new technique is based on negative correlations between optical thickness and terrain height that can be observed if a cloud that is relatively plane-parallel is truncated by the terrain. A validation of the new technique using camera data has shown that the quality of fog detection is comparable to that of another modern fog detection scheme developed and validated for the temperate zones. The method is particularly applicable to optically thinner water clouds. Beyond a cloud optical thickness of ≈ 40, classification errors significantly increase.

Description: The uncertainty of the atmospheric integrated water vapour estimated from GNSS observations Atmospheric Measurement Techniques Discussions, 8, 8817-8857, 2015 Author(s): T. Ning, J. Wang, G. Elgered, G. Dick, J. Wickert, M. Bradke, and M. Sommer Within the Global Climate Observing System (GCOS) Reference Upper Air Network (GRUAN) there is a need for an assessment of the uncertainty in the Integrated Water Vapour (IWV) in the atmosphere estimated from ground-based GNSS observations. All relevant error sources in GNSS-derived IWV is therefore essential to be investigated. We present two approaches, a statistical and a theoretical analysis, for the assessment of the uncertainty of the IWV. It will be implemented to the GNSS IWV data stream for GRUAN in order to obtain a specific uncertainty for each data point. In addition, specific recommendations are made to GRUAN on hardware, software, and data processing practices to minimize the IWV uncertainty. By combining the uncertainties associated with the input variables in the estimations of the IWV, we calculated the IWV uncertainties for several GRUAN sites with different weather conditions. The results show a similar relative importance of all uncertainty contributions where the uncertainties in the Zenith Total Delay (ZTD) dominate the error budget of the IWV contributing with over 75 % to the total IWV uncertainty. The impact of the uncertainty associated with the conversion factor between the IWV and the Zenith Wet Delay (ZWD) is proportional to the amount of water vapour and increases slightly for moist weather conditions. The GRUAN GNSS IWV uncertainty data will provide a quantified confidence to be used for the validation of other measurement techniques, taking the uncertainty into account from diurnal to decadal time scales.

Description: Ground based lidar and microwave radiometry synergy for high vertically resolved thermodynamic profiling Atmospheric Measurement Techniques Discussions, 8, 5467-5509, 2015 Author(s): M. Barrera-Verdejo, S. Crewell, U. Löhnert, E. Orlandi, and P. Di Girolamo Continuous monitoring of atmospheric humidity and temperature profiles is important for many applications, e.g. assessment of atmospheric stability and cloud formation. While lidar measurements can provide high vertical resolution albeit with limited coverage, microwave radiometers receive information throughout the troposphere though their vertical resolution is poor. In order to overcome these specific limitations the synergy of a Microwave Radiometer (MWR) and a Raman Lidar (RL) system is presented in this work. The retrieval algorithm that combines these two instruments is an Optimal Estimation Method (OEM) that allows for a uncertainty analysis of the retrieved profiles. The OEM combines measurements and a priori information taking the uncertainty of both into account. The measurement vector consists of a set of MWR brightness temperatures and RL water vapor profiles. The method is applied for a two month field campaign around Jülich, Germany for clear sky periods. Different experiments are performed to analyse the improvements achieved via the synergy compared to the individual retrievals. When applying the combined retrieval, on average the theoretically determined absolute humidity error can be reduced by 59.8% (37.9%) with respect to the retrieval using only-MWR (only-RL) data. The analysis in terms of degrees of freedom for signal reveals that most information is gained above the usable lidar range. The retrieved profiles are further evaluated using radiosounding and GPS water vapor measurements. Within a single case study we also explore the potential of the OEM for deriving the relative humidity profile, which is especially interesting to study cloud formation in the vicinity of cloud edges. To do so temperature information is added both from RL and MWR. For temperature, it is shown that the error is reduced by 47.1% (24.6%) with respect to the only-MWR (only-RL) profile. Due to the use of MWR brightness temperatures at multiple elevation angles, the MWR provides significant information below the lidar overlap region as shown by the degrees of freedom for signal. Therefore it might be sufficient to combine RL water vapor with multi-angle, multi-wavelength MWR for the retrieval of relative humidity, however, long-term studies are necessary in the future. In general, the benefit of the sensor combination is especially strong in regions where Raman Lidar data is not available (i.e. overlap region, poor signal to noise ratio), whereas if both instruments are available, RL dominates the retrieval.

Description: Effective resolution concepts for lidar observations Atmospheric Measurement Techniques Discussions, 8, 5363-5424, 2015 Author(s): M. Iarlori, F. Madonna, V. Rizi, T. Trickl, and A. Amodeo Since its first establishment in 2000, EARLINET (European Aerosol Research Lidar NETwork) has been devoted to providing, through its database, exclusively quantitative aerosol properties, such as aerosol backscatter and aerosol extinction coefficients, the latter only for stations able to retrieve it independently (from Raman or High Spectral Resolution Lidars). As these coefficients are provided in terms of vertical profiles, EARLINET database must also include the details on the range resolution of the submitted data. In fact, the algorithms used in the lidar data analysis often alter the spectral content of the data, mainly working as low pass filters with the purpose of noise damping. Low pass filters are mathematically described by the Digital Signal Processing (DSP) theory as a convolution sum. As a consequence, this implies that each filter's output, at a given range (or time) in our case, will be the result of a linear combination of several lidar input data relative to different ranges (times) before and after the given range (time): a first hint of loss of resolution of the output signal. The application of filtering processes will also always distort the underlying true profile whose relevant features, like aerosol layers, will then be affected both in magnitude and in spatial extension. Thus, both the removal of noise and the spatial distortion of the true profile produce a reduction of the range resolution. This paper provides the determination of the effective resolution (ERes) of the vertical profiles of aerosol properties retrieved starting from lidar data. Large attention has been addressed to provide an assessment of the impact of low-pass filtering on the effective range resolution in the retrieval procedure.

Description: The stability and calibration of water vapor isotope ratio measurements during long-term deployments Atmospheric Measurement Techniques Discussions, 8, 5425-5466, 2015 Author(s): A. Bailey, D. Noone, M. Berkelhammer, H. C. Steen-Larsen, and P. Sato With the recent advent of commercial laser absorption spectrometers, field studies measuring stable isotope ratios of hydrogen and oxygen in water vapor have proliferated. These pioneering analyses have provided invaluable feedback about best strategies for optimizing instrumental accuracy, yet questions still remain about instrument performance and calibration approaches for multi-year field deployments. With clear scientific potential for using these instruments to carry out long-term monitoring of the hydrological cycle, this study examines the long-term stability of the isotopic biases associated with three cavity-enhanced laser absorption spectrometers – calibrated with different systems and approaches – at two remote field sites: Mauna Loa Observatory, Hawaii, USA, and Greenland Environmental Observatory, Summit, Greenland. The analysis pays particular attention to the stability of measurement dependencies on water vapor concentration and also evaluates whether these so-called concentration-dependences are sensitive to statistical curve-fitting choices or measurement hysteresis. The results suggest evidence of monthly-to-seasonal concentration-dependence variability – which likely stems from low signal-to-noise at the humidity-range extremes – but no long-term directional drift. At Mauna Loa, where the isotopic analyzer is calibrated by injection of liquid water standards into a vaporizer, the largest source of inaccuracy in characterizing the concentration-dependence stems from an insufficient density of calibration points at low humidity. In comparison, at Greenland, the largest source of inaccuracy is measurement hysteresis associated with interactions between the reference vapor, generated by a custom dew point generator (DPG), and the sample tubing. Nevertheless, prediction errors associated with correcting the concentration-dependence are small compared to total measurement uncertainty. At both sites, a dominant source of uncertainty is instrumental precision at low humidity, which cannot be reduced by improving calibration strategies. Challenges in monitoring long-term isotopic drift are also discussed in light of the different calibration systems evaluated.

Description: Complex experiment on stydying the microphysical, chemical, and optical propertires of aerosol particles and estimating the contribution of atmospheric aerosol to Earth radiation budget Atmospheric Measurement Techniques Discussions, 8, 5769-5808, 2015 Author(s): G. G. Matvienko, B. D. Belan, M. V. Panchenko, O. A. Romanovskii, S. M. Sakerin, D. M. Kabanov, S. A. Turchinovich, Y. S. Turchinovich, T. A. Eremina, V. S. Kozlov, S. A. Terpugova, V. V. Pol'kin, E. P. Yausheva, D. G. Chernov, T. B. Zhuravleva, T. V. Bedareva, S. L. Odintsov, V. D. Burlakov, A. V. Nevzorov, M. Yu. Arshinov, G. A. Ivlev, D. E. Savkin, A. V. Fofonov, V. A. Gladkikh, A. P. Kamardin, Yu. S. Balin, G. P. Kokhanenko, I. E. Penner, S. V. Samoilova, P. N. Antokhin, V. G. Arshinova, D. K. Davydov, A. V. Kozlov, D. A. Pestunov, T. M. Rasskazchikova, D. V. Simonenkov, T. K. Sklyadneva, G. N. Tolmachev, S. B. Belan, V. P. Shmargunov, A. S. Kozlov, and S. B. Malyshkin The primary objective of the Complex Aerosol Experiment was measurement of microphysical, chemical, and optical properties of aerosol particles in the surface air layer and free atmosphere. The measurement data were used to retrieve the whole set of aerosol optical parameters, necessary for radiation calculations. Three measurement cycles were performed within the Experiment during 2013: in spring, when the aerosol generation is maximal; in summer (July), when atmospheric boundary layer altitude and, hence, mixing layer altitude are maximal; and in late summer – early autumn, during the period of nucleation of secondary particles. Numerical calculations were compared with measurements of downward solar fluxes on the Earth's surface, performed in the clear-sky atmosphere in summer periods in 2010–2012 in a background region of the boreal zone of Siberia. It has been shown that, taking into account the instrumental errors and errors of atmospheric parameters, the relative differences between model and experimental values of direct and global solar radiation fluxes do not exceed, on the average, 1 and 3%, respectively. Thus, independently obtained data on the optical, meteorological, and microphysical parameters of the atmosphere allows intercalibration and inter-complement of the data and, thereby, provide for qualitatively new information which explains the physical nature of the processes that form the vertical structure of the aerosol field.

Description: Effects of polar stratospheric clouds in the Nimbus 7 LIMS Version 6 data set Ellis Remsberg and V. Lynn Harvey Atmos. Meas. Tech., 9, 2927-2946, doi:10.5194/amt-9-2927-2016, 2016 Emissions from polar stratospheric cloud (PSC) particles affect the retrieved ozone and water vapor from the Limb Infrared Monitor of the Stratosphere (LIMS) satellite experiment. Threshold criteria are applied to the retrieved ozone for the detection and screening of those effects. The PSC effects correlate very well with regions of coldest temperatures (

Description: A Polarimetric Scattering Database for Non-spherical Ice Particles at MicrowaveWavelengths Yinghui Lu, Zhiyuan Jiang, Kultegin Aydin, Johannes Verlinde, Eugene E. Clothiaux, and Giovanni Botta Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2016-228,2016 Manuscript under review for AMT (discussion: open, 0 comments) The database contains the complete(polarimatric) scattering information for different types of ice particles at different incident and scattered radiation directions at 4 microwave wavelengths. These results are useful for understanding the dependence of ice-particle scattering properties on ice-particle orientation with respect to the incident and scattered radiation. It is also useful in ice property retrievals, radar forward simulation.

Description: Identification of the cloud base height over the central Himalayan region: Intercomparison of Ceilometer and Doppler Lidar K. K. Shukla, K. Niranjan Kumar, D. V. Phanikumar, R. K. Newsom, V. R. Kotamarthi, T. B. M. J. Ouarda, and M. V. Ratnam Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2016-162,2016 Manuscript under review for AMT (discussion: open, 0 comments) Estimation of Cloud base height was carried out by using various ground based instruments (Doppler Lidar and Ceilometer) and satellite datasets (MODIS) over central Himalayan region for the first time. The present study demonstrates the potential of Doppler Lidar in precise estimation of cloud base height and updraft velocities. More such deployments will be invaluable inputs for regional weather prediction models over complex Himalayan terrains.

Description: Stratospheric Air Sub-sampler (SAS) and its application to analysis of Δ 17 O(CO 2 ) from small air samples collected with an AirCore Dorota Janina Mrozek, Carina van der Veen, Magdalena E. G. Hofmann, Huilin Chen, Rigel Kivi, Pauli Heikkinen, and Thomas Röckmann Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2016-124,2016 Manuscript under review for AMT (discussion: open, 0 comments) Stratospheric Air Sub-sampler (SAS) is a device to collect and to store the stratospheric profile of air collected with an AirCore (Karion et al, 2010) in numerous sub-samples. The sub-samples (each of 25 mL at ambient temperature and pressure) can be later introduced to the continuous flow systems to measure for example the isotopic composition of CO 2 . The performance of the coupled system is demonstrated for a set of air samples from an AirCore flight in November 2014 near Sodankylä, Finland.

Description: Real time retrieval of volcanic cloud particles and SO 2 by satellite using an improved simplified approach Sergio Pugnaghi, Lorenzo Guerrieri, Stefano Corradini, and Luca Merucci Atmos. Meas. Tech., 9, 3053-3062, doi:10.5194/amt-9-3053-2016, 2016 Volcanic plume removal (VPR) is a procedure developed to retrieve the ash optical depth, effective radius and mass, and sulfur dioxide mass contained in a volcanic cloud from the thermal radiance at 8.7, 11, and 12 µm. It is based on an estimation of a virtual image representing what the sensor would have seen in a multispectral thermal image if the volcanic cloud were not present. Ash and sulfur dioxide were retrieved by the first version of the VPR using a very simple atmospheric model that ignored the layer above the volcanic cloud. This new version takes into account the layer of atmosphere above the cloud as well as thermal radiance scattering along the line of sight of the sensor. In addition to improved results, the new version also offers an easier and faster preliminary preparation and includes other types of volcanic particles (andesite, obsidian, pumice, ice crystals, and water droplets). As in the previous version, a set of parameters regarding the volcanic area, particle types, and sensor is required to run the procedure. However, in the new version, only the mean plume temperature is required as input data. In this work, a set of parameters to compute the volcanic cloud transmittance in the three quoted bands, for all the aforementioned particles, for both Mt. Etna (Italy) and Eyjafjallajökull (Iceland) volcanoes, and for the Terra and Aqua MODIS instruments is presented. Three types of tests are carried out to verify the results of the improved VPR. The first uses all the radiative transfer simulations performed to estimate the above mentioned parameters. The second one makes use of two synthetic images, one for Mt. Etna and one for Eyjafjallajökull volcanoes. The third one compares VPR and Look-Up Table (LUT) retrievals analyzing the true image of Eyjafjallajökull volcano acquired by MODIS aboard the Aqua satellite on 11 May 2010 at 14:05 GMT.

Description: Evaluation of IWV from the numerical weather prediction WRF model with PPP GNSS processing for Bulgaria Tzvetan Simeonov, Dmitry Sidorov, Felix Norman Teferle, Georgi Milev, and Guergana Guerova Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2016-152,2016 Manuscript under review for AMT (discussion: open, 0 comments) Global Navigation Satellite Systems (GNSS) meteorology is an established operational service providing hourly updated GNSS tropospheric products to the National Meteorologic Services (NMS) in Europe. In the last decade through the ground-based GNSS network densification and new processing strategies like Precise Point Positioning (PPP) it has become possible to obtain sub-hourly tropospheric products for monitoring severe weather events. In this work one year (January–December 2013) of sub-hourly GNSS tropospheric products (Zenith Total Delay) are computed using the PPP strategy for seven stations in Bulgaria. In order to take advantage of the sub-hourly GNSS data to derive Integrated Water Vapour (IWV) surface pressure and temperature with similar temporal resolution is required. As the surface observations are on 3 hourly basis the first step is to compare the surface pressure and temperature from numerical weather prediction model Weather Forecasting and Research (WRF) with observations at three synoptic stations in Bulgaria. The mean difference between the two data-sets for 1) surface pressure is less than 0.5 hPa and the correlation is over 0.989, 2) temperature the largest mean difference is 1.1 °C and the correlation coefficient is over 0.957 and 3) IWV mean difference is in range 0.1–1.1 mm. The evaluation of WRF on annual bases shows IWV underestimation between 0.5 and 1.5 mm at five stations and overestimation at Varna and Rozhen. Varna and Rozhen have also much smaller correlation 0.9 and 0.76. The study of the monthly IWV variation shows that at those locations the GNSS IWV has unexpected drop in April and March respectively. The reason for this drop is likely problems with station raw data. At the remaining 5 stations a very good agreement between GNSS and WRF is observed with high correlation during the cold part of 2013 i.e. March, October and December (0.95) and low correlation during the warm part of 2013 i.e. April to August (below 0.9). The diurnal cycle of the WRF model shows a dry bias in the range of 0.5-1.5 mm. Between 00 and 01 UTC the GNSS IWV tends to be underestimate IWV which is likely due to the processing window used. The precipitation efficiency from GNSS and WRF show very good agreement on monthly bases with a maximum in May-June and minimum in August–September. The annual precipitation efficiency in 2013 at Lovech and Burgas is about 6 %.

Description: Comparison of MODIS and VIIRS cloud properties with ARM ground-based observations over Finland Moa K. Sporre, Ewan J. O'Connor, Nina Håkansson, Anke Thoss, Erik Swietlicki, and Tuukka Petäjä Atmos. Meas. Tech., 9, 3193-3203, doi:10.5194/amt-9-3193-2016, 2016 Satellite measurements of cloud top height and liquid water path are compared to ground-based remote sensing to evaluate the satellite retrievals. The overall performance of the satellite retrievals of cloud top height are good, but they become more problematic when several layers of clouds are present. The liquid water path retrievals also agree well, and the average differences are within the estimated measurement uncertainties.

Description: Remote sensing of tropospheric turbulence using GPS radio occultation Esayas Shume and Chi Ao Atmos. Meas. Tech., 9, 3175-3182, doi:10.5194/amt-9-3175-2016, 2016 Radio occultation (RO) measurements are sensitive to the small-scale irregularities in the atmosphere. In this study, we present a new technique to estimate tropospheric turbulence strength (namely, scintillation index) by analyzing RO amplitude fluctuations in impact parameter domain. GPS RO observations from the COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate) satellites enabled us to calculate global maps of scintillation measures, revealing the seasonal, latitudinal, and longitudinal characteristics of the turbulent troposphere. Such information are both difficult and expensive to obtain especially over the oceans. To verify our approach, simulation experiments using the multiple phase screen (MPS) method were conducted. The results show that scintillation indices inferred from the MPS simulations are in good agreement with scintillation measures estimated from COSMIC observations.

Description: CFC-11, CFC-12 and HCFC-22 ground-based remote sensing FTIR measurements at Reunion Island and comparisons with MIPAS/ENVISAT data Minqiang Zhou, CCorinne Vigouroux, Bavo Langerock, Pucai Wang, Geoff Dutton, Christian Hermans, Nicolas Kumps, Jean-Marc Metzger, Geoff Toon, and Martine De Mazière Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2016-235,2016 Manuscript under review for AMT (discussion: open, 0 comments) Profiles of CFC-11, CFC-12 and HCFC-22 have been obtained from FTIR measurements above the Saint-Denis and Maïdo sites at Reunion Island (21ºS, 55ºE) with low vertical resolution. The trends derived from the FTIR measurements are -0.86±0.12% and 2.75±0.12% for CFC-11 and HCFC-22, respectively, for the period 2004 to 2016 , and -0.76±0.05% for CFC-12 for 2009 to 2016, which are consistent with ground-based in-situ observations. Our FTIR data and the collocated MIPAS data are in good agreement.

Description: Evaluation And Attribution Of OCO-2 XCO 2 Uncertainties John Worden, Gary Doran, Susan Kulawik, Annmarie Eldering, David Crisp, Chris Frankenberg, Christian O'Dell, and Kevin Bowman Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2016-175,2016 Manuscript under review for AMT (discussion: open, 0 comments) This paper evaluates the uncertainties of the total column carbon dioxide (XCO 2 ) measurements from the NASA OCO-2 instrument by comparing observed variations in small geographical regions to the calculated uncertainties of the data within this region. In general we find that the XCO 2 uncertainties are consistent with calculated values of approximately 0.2 ppm over the ocean whereas variations over land likely have larger uncertainties of at least ~ 0.7 ppm.

Description: Vertical profiles of aerosol optical properties and the solar heating rate estimated by combining sky radiometer and lidar measurements Rei Kudo, Tomoaki Nishizawa, and Toshinori Aoyagi Atmos. Meas. Tech., 9, 3223-3243, doi:10.5194/amt-9-3223-2016, 2016 An algorithm for estimating the vertical profiles of the aerosol physical and optical properties, and the solar heating rate from combining sky radiometer and lidar measurements was proposed. The validity and performance of the algorithm were shown by the intensive sensitivity tests using simulated data for different aerosol profiles and the application to the actual measurements in Tsukuba, Japan.

Description: Intercomparison of aerosol extinction profiles retrieved from MAX-DOAS measurements U. Frieß, H. Klein Baltink, S. Beirle, K. Clémer, F. Hendrick, B. Henzing, H. Irie, G. de Leeuw, A. Li, M. M. Moerman, M. van Roozendael, R. Shaiganfar, T. Wagner, Y. Wang, P. Xie, S. Yilmaz, and P. Zieger Atmos. Meas. Tech., 9, 3205-3222, doi:10.5194/amt-9-3205-2016, 2016 This article describes the first direct comparison of aerosol extinction profiles from Multi-Axis DOAS measurements of the oxygen collision complex using five different retrieval algorithms. A comparison of the retrieved profiles with co-located aerosol measurements shows good agreement with respect to profile shape and aerosol optical thickness. This study shows that MAX-DOAS is a simple, versatile and cost-effective method for the measurement of aerosol properties in the lower troposphere.

Description: Assessing the Performance of Troposphere Tomographic Modeling Using Multi-Source Water Vapor Data During Hong Kong’s Rainy Season from May to October 2013 Biyan Chen and Zhizhao Liu Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2016-158,2016 Manuscript under review for AMT (discussion: open, 0 comments) A multi-source water vapor tomography model is developed using data from GPS (Global Positioning System), radiosonde, WVR (Water Vapor Radiometer), NWP (Numerical Weather Prediction), AERONET (AErosol RObotic NETwork) sunphotometer and synoptic stations. Results show that the assimilation of multi-source data can increase the quality of tomographic solution. Evaluation shows that tomography model is robust during heavy rain conditions and it can contribute to severe weather forecasting.

Description: Identification of Tower Wake Distortions Using Sonic Anemometer and Lidar Measurements Katherine McCaffrey, Paul Quelet, Aditya Choukulkar, James M. Wilczak, Daniel E. Wolfe, Steven Oncley, Alan Brewer, Mithu Debnath, Ryan Ashton, G. Valerio Iungo, and Julie K. Lundquist Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2016-179,2016 Manuscript under review for AMT (discussion: open, 0 comments) During the eXperimental Planetary boundary layer Instrumentation Assessment (XPIA) field campaign, the wake and flow distortion from a 300-meter meteorological tower was identified using pairs of sonic anemometers mounted on opposite sides of the tower, as well as profiling and scanning lidars. Wind speed deficits up to 50 % and TKE increases of two orders of magnitude were observed at wind directions in the wake, along with wind direction differences (flow deflection) outside of the wake.

Description: Simulation study for measurement of horizontal wind profiles in the polar stratosphere and mesosphere using ground-based observations of ozone and carbon monoxide lines in the 230–250 GHz region David A. Newnham, George P. Ford, Tracy Moffat-Griffin, and Hugh C. Pumphrey Atmos. Meas. Tech., 9, 3309-3323, doi:10.5194/amt-9-3309-2016, 2016 We demonstrate the feasibility of measuring polar atmospheric winds over the altitude range 23–97 km using ground-based millimetre-wave Doppler radiometry. Atmospheric and instrument simulations were carried out for Halley station, Antarctica. This remote sensing technique will provide continuous horizontal wind observations in the stratosphere and mesosphere where measurements are currently very limited. The data are needed for meteorological analyses and atmospheric modelling applications.

Description: Chamber catalogues of optical and fluorescent signatures distinguish bioaerosol classes Mark Hernandez, Anne E. Perring, Kevin McCabe, Greg Kok, Gary Granger, and Darrel Baumgardner Atmos. Meas. Tech., 9, 3283-3292, doi:10.5194/amt-9-3283-2016, 2016 We have performed laboratory experiments examining a large set of known bacterial, fungal and pollen species using a Wideband Integrated Bioaerosol Sensor (WIBS). The instrumental response is shown to be sufficiently distinct for these classes of particles to distinguish between them, and this library will provide a framework for interpretation of UV-induced fluorescence measurements of atmospheric bioaerosol. Atmospheric implications and instrumental considerations are discussed.

Description: Improved Methodologies for Continuous Flow Analysis of Stable Water Isotopes in Ice Cores Tyler R. Jones, James W. C. White, Eric J. Steig, Bruce H. Vaughn, Valerie Morris, Vasileios Gkinis, Bradley R. Markle, and Spruce W. Schoenemann Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2016-118,2016 Manuscript under review for AMT (discussion: open, 0 comments) New systems have been developed that continuously melt ice core samples, in contrast to other methods that analyze a single sample at a time. These newer systems are capable of reducing analysis time by many years and improving data set resolution. In this study, we introduce improved methodologies that optimize the speed, accuracy, and precision of a water isotope continuous flow system. The presented system will be used for Antarctic and Greenland ice core projects.

Description: Validation of COSMIC water vapor data in the upper troposphere and lower stratosphere using MLS, MERRA and ERA-Interim Ming Shangguan, Katja Matthes, Wuke Wang, and Tae-Kwon Wee Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2016-248,2016 Manuscript under review for AMT (discussion: open, 0 comments) A first validation of the COSMIC Radio Occultation (RO) water vapor data in the upper troposphere and lower stratosphere (UTLS) are presented in this paper. The COSMIC water vapor shows a good agreement with the Microwave limb Sounder (MLS) in both the spatial distribution and the seasonal to interannual variations. It is very valuable for studying the water vapor in the UTLS, thanks to its global coverage, all- weather aptitude and high vertical resolution.

Description: Harmonization and Diagnostics of MIPAS ESA CH 4 and N 2 O Profiles Using Data Assimilation Quentin Errera, Simone Ceccherini, Yves Christophe, Simon Chabrillat, Michaela I. Hegglin, Alyn Lambert, Richard Ménard, Piera Raspollini, Sergey Skachko, Michiel van Weele, and Kaley A. Walker Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2016-245,2016 Manuscript under review for AMT (discussion: open, 0 comments) This paper discusses assimilation experiments of methane (CH 4 ) and nitrous oxide (N 2 O) profiles observed by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS). Here we focus on data versions 6 and 7 retrieved by the ESA processor. These datasets have been assimilated by the Belgian Assimilation System for Chemical ObsErvations (BASCOE). The CH 4 and N 2 O profiles can be noisy especially in the tropical lower stratosphere. Using the averaging kernels of the observations and a background error covariance matrix – the B matrix, which has been previously calibrated, allows the system to partly remedy this issue and provide assimilated fields that are more regular vertically. In general, there is a good agreement between the BASCOE analyses and independent observations demonstrating the general good quality of these two retrievals provided by MIPAS ESA. Nevertheless, this study also identifies two issues in these datasets. First, time-series of the observations show unexpected discontinuities, due to the calibration method used for the level-1 data. Second, the correlations between BASCOE analyses and independent observations are poor in the lower stratosphere, especially in the tropics, probably due to the presence of outliers in the assimilated data. In this region, we recommend using MIPAS CH 4 and N 2 O observations with caution.

Description: Sampling strategies and post-processing methods for increasing the time resolution of organic aerosol measurements requiring long sample-collection times Rob L. Modini and Satoshi Takahama Atmos. Meas. Tech., 9, 3337-3354, doi:10.5194/amt-9-3337-2016, 2016 Aerosol measurement techniques with high detection limits often result in poorly time-resolved measurements. We investigated sampling strategies and post-processing methods for constructing hourly resolved aerosol concentration time series from samples collected for 4 to 8 h. We show that this is an effective way to increase measurement time resolution, and that under realistic experimental conditions, simple methods can perform as well as more sophisticated methods.

Description: The Moon as a photometric calibration standard for microwave sensors Martin Burgdorf, Stefan A. Buehler, Theresa Lang, Simon Michel, and Imke Hans Atmos. Meas. Tech., 9, 3467-3475, doi:10.5194/amt-9-3467-2016, 2016 The upper-tropospheric humidity is an essential climate variable, which can be measured with microwave sounders in polar orbits. A stable photometric calibration of these instruments is indispensable for detecting long-term trends. We demonstrate that this can be achieved by using the Moon in a fixed phase as a flux standard for dedicated pitch maneuver observations. This method is particularly suited for future sensors with small beamwidths.

Description: A new approach for retrieving the UV–vis optical properties of ambient aerosols Nir Bluvshtein, J. Michel Flores, Lior Segev, and Yinon Rudich Atmos. Meas. Tech., 9, 3477-3490, doi:10.5194/amt-9-3477-2016, 2016 Understanding spectrally dependent optical properties of aerosols is needed to quantify the effective radiative forcing due to aerosol–radiation interactions. We describe a new approach to retrieve extensive and intensive optical properties of the aerosol population over 300 to 650 nm wavelength. This new approach was validated with retrieval simulations, laboratory and continuous ambient aerosols measurements. Results showed low errors and good agreement with expected values.

Description: Bias corrections of GOSAT SWIR XCO 2 and XCH 4 with TCCON data and their evaluation using aircraft measurement data Makoto Inoue, Isamu Morino, Osamu Uchino, Takahiro Nakatsuru, Yukio Yoshida, Tatsuya Yokota, Debra Wunch, Paul O. Wennberg, Coleen M. Roehl, David W. T. Griffith, Voltaire A. Velazco, Nicholas M. Deutscher, Thorsten Warneke, Justus Notholt, John Robinson, Vanessa Sherlock, Frank Hase, Thomas Blumenstock, Markus Rettinger, Ralf Sussmann, Esko Kyrö, Rigel Kivi, Kei Shiomi, Shuji Kawakami, Martine De Mazière, Sabrina G. Arnold, Dietrich G. Feist, Erica A. Barrow, James Barney, Manvendra Dubey, Matthias Schneider, Laura T. Iraci, James R. Podolske, Patrick W. Hillyard, Toshinobu Machida, Yousuke Sawa, Kazuhiro Tsuboi, Hidekazu Matsueda, Colm Sweeney, Pieter P. Tans, Arlyn E. Andrews, Sebastien C. Biraud, Yukio Fukuyama, Jasna V. Pittman, Eric A. Kort, and Tomoaki Tanaka Atmos. Meas. Tech., 9, 3491-3512, doi:10.5194/amt-9-3491-2016, 2016 In this study, we correct the biases of GOSAT XCO 2 and XCH 4 using TCCON data. To evaluate the effectiveness of our correction method, uncorrected/corrected GOSAT data are compared to independent XCO 2 and XCH 4 data derived from aircraft measurements. Consequently, we suggest that this method is effective for reducing the biases of the GOSAT data. We consider that our work provides GOSAT data users with valuable information and contributes to the further development of studies on greenhouse gases.

Description: Detection of formaldehyde emissions from an industrial zone in the Yangtze-River-Delta region of China using a proton transfer reaction ion-drift chemical ionization mass spectrometer Yan Ma, Yiwei Diao, Bingjie Zhang, Weiwei Wang, Xinrong Ren, Dongsen Yang, Ming Wang, Xiaowen Shi, and Jun Zheng Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2016-194,2016 Manuscript under review for AMT (discussion: open, 0 comments) Here we reported the development of a PTR-ID-CIMS to investigate industry-related emissions of VOCs in the Yangtze-River-Delta (YRD) region, the largest economic zone in China. We observed strong primary HCHO emissions from the industrial zone that overwhelmed local HCHO secondary formation. These primary HCHO sources can potentially lead to severe local and regional air pollution formation. Therefore, primary industrial HCHO emissions should be strictly monitored and regulated in this region.

Description: HoloGondel: in-situ cloud observations on a cable car in the Swiss Alps using a holographic imager Alexander Beck, Jan Henneberger, Sarah Schöpfer, and Ulrike Lohmann Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2016-216,2016 Manuscript under review for AMT (discussion: open, 0 comments) In-situ observations of cloud properties in complex alpine terrain are commonly conducted at mountain-top research stations and limited to single-point measurements. The HoloGondel platform overcomes this limitation by using a cable car to obtain vertical profiles of the microphysical and meteorological cloud parameters. In this work example measurements of the vertical profiles observed in a liquid cloud and a mixed-phase cloud at the Eggishorn in the Swiss Alps are presented.

Description: Satellite observation of atmospheric methane: intercomparison between AIRS and GOSAT TANSO-FTS retrievals Mingmin Zou, Xiaozhen Xiong, Naoko Saitoh, Juying Warner, Ying Zhang, Liangfu Chen, Fuzhong Weng, and Meng Fan Atmos. Meas. Tech., 9, 3567-3576, doi:10.5194/amt-9-3567-2016, 2016 Both AIRS and GOSAT TANSO-FTS TIR have been used to retrieve atmosphere CH 4 . The purpose of an intercomparison is to provide useful information to users on the characteristics of these two different products when they investigate the spatial and temporal variation of CH 4 . On the other hand, AIRS V6 CH 4 data were already validated by comparing with aircraft data. This intercomparison is also a kind of indirect validation to GOSAT data.

Description: Assessment of errors and biases in retrievals of X CO 2 , X CH 4 , X CO , and X N 2 O from a 0.5 cm –1 resolution solar-viewing spectrometer Jacob K. Hedelius, Camille Viatte, Debra Wunch, Coleen M. Roehl, Geoffrey C. Toon, Jia Chen, Taylor Jones, Steven C. Wofsy, Jonathan E. Franklin, Harrison Parker, Manvendra K. Dubey, and Paul O. Wennberg Atmos. Meas. Tech., 9, 3527-3546, doi:10.5194/amt-9-3527-2016, 2016 Portable FTS instruments with lower resolution are being used to measure gases (including CO 2 , CH 4 , CO, and N 2 O) in the atmosphere. We compared measurements from four of these instruments for a few weeks, and with one for nearly a year to a higher resolution TCCON standard. We also performed tests to assess performance under different atmospheric and instrumental conditions. We noted consistent offsets in the short-term (~1 month); more research is still needed to assess precision longer term.

Description: Information Content and Sensitivity of the 3β + 2α Lidar Measurement System for Aerosol Microphysical Retrievals Sharon P. Burton, Eduard Chemyakin, Xu Liu, Kirk Knobelspiesse, Snorre Stamnes, Patricia Sawamura, Richard H. Moore, Chris A. Hostetler, and Richard A. Ferrare Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2016-240,2016 Manuscript under review for AMT (discussion: open, 0 comments) Retrievals of aerosol microphysics exist for ground-based, airborne, and future space-borne lidar measurements. We investigate the information content of a lidar measurement system, using only a forward model but no explicit inversion. The simplified aerosol used here is applicable as a best case for all retrievals in the absence of additional constraints. We report (1) information content of the measurements; (2) uncertainties on the retrieved parameters; and (3) sources of compensating errors.

Description: How to reliably detect molecular clusters and nucleation mode particles with Neutral cluster and Air Ion Spectrometer (NAIS) Hanna E. Manninen, Sander Mirme, Aadu Mirme, Tuukka Petäjä, and Markku Kulmala Atmos. Meas. Tech., 9, 3577-3605, doi:10.5194/amt-9-3577-2016, 2016 This paper reports a standard operation procedure (SOP) for a Neutral cluster and Air Ion Spectrometer (NAIS) to detect small clusters and nucleation mode particles. The NAIS measures number size distributions of charged and neutral aerosol particles. The SOP is needed to provide comparable results measured by NAIS users around the world. The work is based on discussions between the NAIS users (lead by University of Helsinki, Finland) and the NAIS manufacturer (Airel Ltd., Estonia).

Description: Validation of Aura MLS retrievals of temperature, water vapour and ozone in the upper troposphere and lower–middle stratosphere over the Tibetan Plateau during boreal summer Xiaolu Yan, Jonathon S. Wright, Xiangdong Zheng, Nathaniel J. Livesey, Holger Vömel, and Xiuji Zhou Atmos. Meas. Tech., 9, 3547-3566, doi:10.5194/amt-9-3547-2016, 2016 We evaluate Aura Microwave Limb Sounder retrievals of temperature, water vapour and ozone over the eastern Tibetan Plateau against measurements from balloon-borne instruments. The newest version of the retrievals (v4) represents a slight improvement over the previous version, particularly with respect to data yields and upper tropospheric ozone. We identify several biases that did not appear in evaluations conducted elsewhere, highlighting the unique challenges of remote sensing in this region.

Description: The ALTIUS mission Didier Fussen, Emmanuel Dekemper, Quentin Errera, Ghislain Franssens, Nina Mateshvili, Didier Pieroux, and Filip Vanhellemont Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2016-213,2016 Manuscript under review for AMT (discussion: open, 0 comments) Recently, the ALTIUS mission has been declared as an element compliant to the ESA Earth Watch programme. The paper identifies the general scientific context of the project and derives the mission, instrument and scientific products requirements. The general design of the payload and platform systems is discussed. The preliminary data processing chain is presented, from telemetry data to retrieved geophysical profiles, with a complementary data assimilation level.

Description: Intercomparison study and optical asphericity measurements of small ice particles in the CERN CLOUD experiment Leonid Nichman, Emma Järvinen, James Dorsey, Paul Connolly, Jonathan Dupplisy, Claudia Fuchs, Karoliina Ignatius, Kamalika Sengupta, Frank Stratmann, Ottmar Möhler, Martin Schnaiter, and Martin Gallagher Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2016-205,2016 Manuscript under review for AMT (discussion: open, 0 comments) Optical probes are frequently used for the detection of cloud particles. The detected microphysical properties may affect particle growth and accretion mechanisms and the light scattering properties of cirrus clouds. In the CLOUD chamber study at CERN, we compared four optical measurement techniques. We show that shape derivation alone is not sufficient to determine the phase of the small cloud particles. Surface complexity was found to be an important parameter for phase discrimination.

Description: An empirical method to correct for temperature-dependent variations in the overlap function of CHM15k ceilometers Maxime Hervo, Yann Poltera, and Alexander Haefele Atmos. Meas. Tech., 9, 2947-2959, doi:10.5194/amt-9-2947-2016, 2016 Imperfections in a lidar's overlap function lead to artefacts in the lidar (Light Detection and Ranging) signals. These artefacts can erroneously be interpreted as an aerosol gradient or, in extreme cases, as a cloud base leading to false cloud detection. In this study an algorithm is presented to correct such artefacts. The algorithm is completely automatic and does not require any intervention on site. It is therefore suited for use in large automatic lidar networks.

Description: EARLINET Single Calculus Chain – technical – Part 2: Calculation of optical products Ina Mattis, Giuseppe D'Amico, Holger Baars, Aldo Amodeo, Fabio Madonna, and Marco Iarlori Atmos. Meas. Tech., 9, 3009-3029, doi:10.5194/amt-9-3009-2016, 2016 We present an automated software tool for the retrieval of profiles of optical particle properties from lidar signals. This tool is one of the modules of the Single Calculus Chain of the European Aerosol Research Lidar Network (EARLINET). It allows for the analysis of the data of many different lidar systems of EARLINET in an automated, unsupervised way.

Description: The role of cloud contamination, aerosol layer height and aerosol model in the assessment of the OMI near-UV retrievals over the ocean Santiago Gassó and Omar Torres Atmos. Meas. Tech., 9, 3031-3052, doi:10.5194/amt-9-3031-2016, 2016 Aerosol optical depths derived by the OMI near-UV algorithm are evaluated against independent observations over the ocean. The comparison resulted in differences within the expected levels of uncertainty. In addition, in clear sky conditions, the retrieved AODs compare well with independent measurements but they are biased high in partially cloud-contaminated pixels. Additional sources of discrepancies are documented and will be corrected in future versions of the algorithm.

Description: Intercomparison of total column ozone data from the Pandora spectrophotometer with Dobson, Brewer, and OMI measurements over Seoul, Korea Jiyoung Kim, Jhoon Kim, Hi-Ku Cho, Jay Herman, Sang Seo Park, HyunKwang Lim, Jae-hwan Kim, and Koji Miyagawa Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2016-146,2016 Manuscript under review for AMT (discussion: open, 0 comments) Total column ozone (TCO) has been obtained by various ground-based and spaceborne instruments with high accuracy. Here, daily TCO measured by Pandora spectrophotometer (#19) installed since (DRAGON)-NE Asia Campaign (2012) was intercompared using Dobson (#124), Brewer (#148) and OMI measurements from March 2012 to March 2014 at Yonsei University, Seoul, Korea. And the result showed that Pandora TCO is in highly good agreement with other measurements.

Description: Benchmark campaign and case study episode in central Europe for development and assessment of advanced GNSS tropospheric models and products Jan Douša, Galina Dick, Michal Kačmařík, Radmila Brožková, Florian Zus, Hugues Brenot, Anastasia Stoycheva, Gregor Möller, and Jan Kaplon Atmos. Meas. Tech., 9, 2989-3008, doi:10.5194/amt-9-2989-2016, 2016 GNSS products provide observations of atmospheric water vapour. Advanced tropospheric products focus on ultra-fast and high-resolution zenith total delays (ZTDs), horizontal gradients and slant delays, all suitable for rapid-cycle numerical weather prediction (NWP) and severe weather event monitoring. The GNSS4SWEC Benchmark provides a complex data set for developing and assessing these products, with initial focus on reference ZTDs and gradients derived from several NWP and dense GNSS networks.

Description: Operation of the Airmodus A11 nano Condensation Nucleus Counter at various inlet pressures and various operation temperatures, and design of a new inlet system Juha Kangasluoma, Alessandro Franchin, Jonahtan Duplissy, Lauri Ahonen, Frans Korhonen, Michel Attoui, Jyri Mikkilä, Katrianne Lehtipalo, Joonas Vanhanen, Markku Kulmala, and Tuukka Petäjä Atmos. Meas. Tech., 9, 2977-2988, doi:10.5194/amt-9-2977-2016, 2016 The paper describes technical aspects of using the Airmodus A11 nCNC at various inlet pressures and how temperature selection affects the performance of the instrument. We also present a sampling box to minimize the inlet losses and make use of the instrument more convenient.

Description: Effect of secondary organic aerosol coating thickness on the real-time detection and characterization of biomass burning soot by two particle mass spectrometers Adam T. Ahern, R. Subramanian, Georges Saliba, Eric M. Lipsky, Neil M. Donahue, and Ryan C. Sullivan Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2016-201,2016 Manuscript under review for AMT (discussion: open, 0 comments) The SP-AMS exhibited a different sensitivity to black carbon versus potassium as more SOA mass was condensed onto biomass burning particles. The SP-AMS’s sensitivity to BC mass did not plateau following successive SOA coatings, despite achieving high OA : BC mass ratios 〉 9. A laser ablation single-particle mass spectrometer exhibited a linear response to the condensed SOA mass on individual soot particles, demonstrating its ability to obtain mass quantitative measurements from complex matrices.

Description: Comparison of the Arctic upper-air temperatures from radiosonde and radio occultation observations Liang Chang, Lixin Guo, Guiping Feng, Xuerui Wu, and Guoping Gao Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2016-232,2016 Manuscript under review for AMT (discussion: open, 0 comments) Air temperature is one of the most important parameters used for monitoring Arctic climate change. The Constellation Observing System for Meteorology, Ionosphere, and Climate and Formosa Satellite mission 3 (COSMIC/FORMOSAT-3) radio occultation (RO) "wet" temperature product (i.e., "wetPrf") was introduced to analyze the Arctic air temperature profiles at 925–200 hPa in 2007–2012. The "wet" temperatures were further compared with radiosonde (RS) observations. Results from the spatially and temporally synchronized RS and COSMIC observations showed that their temperatures were matched well with each other, especially at 400 hPa. Comparisons of seasonal temperatures and anomalies from COSMIC and homogenized RS observations suggested the limited number of COSMIC observations during the spatial matchup may be insufficient to describe the small-scale spatial structure of temperature variations. Furthermore, comparisons of seasonal temperature anomalies from RS and 5 × 5 degree gridded COSMIC observations at 400 hPa during the sea ice minimum (SIM) of 2007 and 2012 were also made. Results revealed that the widely covered COSMIC observations can provide more details than RS observations in describing the Arctic temperature variations. Therefore, despite COSMIC observations being unsuitable to describe the Arctic temperatures in the lowest level, they provide a complementary data source to study the Arctic upper-air temperature variations and related climate change.

Description: Direct assimilation of Chinese FY-3C Microwave Temperature Sounder-2 radiances in the global GRAPES system Juan Li and Guiqing Liu Atmos. Meas. Tech., 9, 3095-3113, doi:10.5194/amt-9-3095-2016, 2016 FengYun-3C is an operational polar-orbiting satellite carrying the new-generation microwave sounding instruments in China. It can contribute to the Global Environmental Observing System of Systems. It is anticipated that the data can be useful for the weather forecast. After quality control, the data are put into the Chinese numerical weather prediction (NWP) system. It shows that the microwave temperature observations can have a neutral to positive impact on the NWP system.

Description: Characterization of anthropogenic methane plumes with the Hyperspectral Thermal Emission Spectrometer (HyTES): a retrieval method and error analysis Le Kuai, John R. Worden, King-Fai Li, Glynn C. Hulley, Francesca M. Hopkins, Charles E. Miller, Simon J. Hook, Riley M. Duren, and Andrew D. Aubrey Atmos. Meas. Tech., 9, 3165-3173, doi:10.5194/amt-9-3165-2016, 2016 This paper describes the retrieval algorithm to estimate the lower tropospheric methane concentrations using Hyperspectral Thermal Emission Spectrometer (HyTES) airborne measurements. This project aims to map and detect methane plumes from the oil leaking or dairy emission. Our results demonstrate an example of the quantitative retrievals, imaged a big methane plume from storage tanks near Kern River Oil Field. The methane enhancement is well above the uncertainties of the estimates.

Description: Improved analysis of solar signals for differential reflectivity monitoring Asko Huuskonen, Mikko Kurri, and Iwan Holleman Atmos. Meas. Tech., 9, 3183-3192, doi:10.5194/amt-9-3183-2016, 2016 The method for the daily monitoring of the differential reflectivity bias for polarimetric weather radars is developed further. Improved quality control is applied to the solar signals detected during the operational scanning of the radar, which efficiently removes rain and clutter-contaminated gates occurring in the solar hits. The simultaneous reflectivity data are used as a proxy to determine which data points are to be removed. A number of analysis methods to determine the differential reflectivity bias are compared, and methods based on surface fitting are found superior to simple averaging. A separate fit to the reflectivity of the horizontal and vertical polarization channels is recommended because of stability. Separate fitting also provides, in addition to the differential reflectivity bias, the pointing difference of the polarization channels. Data from the Finnish weather radar network show that the pointing difference is less than 0.02° and that the differential reflectivity bias is stable and determined to better than 0.04 dB. The results are compared to those from measurements at vertical incidence, which allows us to determine the total differential reflectivity bias including the differential receiver bias and the transmitter bias.

Description: Ion mobility spectrometry–mass spectrometry (IMS–MS) for on- and offline analysis of atmospheric gas and aerosol species Jordan E. Krechmer, Michael Groessl, Xuan Zhang, Heikki Junninen, Paola Massoli, Andrew T. Lambe, Joel R. Kimmel, Michael J. Cubison, Stephan Graf, Ying-Hsuan Lin, Sri H. Budisulistiorini, Haofei Zhang, Jason D. Surratt, Richard Knochenmuss, John T. Jayne, Douglas R. Worsnop, Jose-Luis Jimenez, and Manjula R. Canagaratna Atmos. Meas. Tech., 9, 3245-3262, doi:10.5194/amt-9-3245-2016, 2016 Measurement techniques that provide molecular-level information are needed to elucidate the multiphase processes that produce secondary organic aerosol (SOA) species in the atmosphere. Here we demonstrate the application of ion mobility spectrometry-mass spectrometry (IMS–MS) to the simultaneous characterization of the elemental composition and molecular structures of organic species in the gas and particulate phases. Molecular ions of gas-phase organic species are measured online with IMS–MS after ionization with a custom-built nitrate chemical ionization (CI) source. This CI–IMS–MS technique is used to obtain time-resolved measurements (5 min) of highly oxidized organic molecules during the 2013 Southern Oxidant and Aerosol Study (SOAS) ambient field campaign in the forested SE US. The ambient IMS–MS signals are consistent with laboratory IMS–MS spectra obtained from single-component carboxylic acids and multicomponent mixtures of isoprene and monoterpene oxidation products. Mass-mobility correlations in the 2-D IMS–MS space provide a means of identifying ions with similar molecular structures within complex mass spectra and are used to separate and identify monoterpene oxidation products in the ambient data that are produced from different chemical pathways. Water-soluble organic carbon (WSOC) constituents of fine aerosol particles that are not resolvable with standard analytical separation methods, such as liquid chromatography (LC), are shown to be separable with IMS–MS coupled to an electrospray ionization (ESI) source. The capability to use ion mobility to differentiate between isomers is demonstrated for organosulfates derived from the reactive uptake of isomers of isoprene epoxydiols (IEPOX) onto wet acidic sulfate aerosol. Controlled fragmentation of precursor ions by collisionally induced dissociation (CID) in the transfer region between the IMS and the MS is used to validate MS peak assignments, elucidate structures of oligomers, and confirm the presence of the organosulfate functional group.

Description: A surface reflectance scheme for retrieving aerosol optical depth over urban surfaces in MODIS Dark Target retrieval algorithm Pawan Gupta, Robert C. Levy, Shana Mattoo, Lorraine A. Remer, and Leigh A. Munchak Atmos. Meas. Tech., 9, 3293-3308, doi:10.5194/amt-9-3293-2016, 2016 A new surface scheme inside MODIS dark target aerosol retrieval algorithm has been developed to improve the accuracy of aerosol optical depth data over cities. The new scheme integrates the MODIS land surface reflectance and land cover type information into the surface parameterization for urban areas, much of the issues associated with the standard algorithm have been mitigated for our test region. The improved aerosols data sets will be useful for air quality applications over cities.

Description: Tropical tropospheric ozone columns from nadir retrievals of GOME-1/ERS-2, SCIAMACHY/Envisat, and GOME-2/MetOp-A (1996–2012) Elpida Leventidou, Kai-Uwe Eichmann, Mark Weber, and John P. Burrows Atmos. Meas. Tech., 9, 3407-3427, doi:10.5194/amt-9-3407-2016, 2016 Here, we present a 17 years tropical tropospheric ozone columns dataset (1996–2012) using GOME, SCIAMACHY, and GOME-2 data, developed as part of the verification algorithm for TROPOMI on S5p mission.The uncertainty is less than 2 DU. Validation with SHADOZ ozonesonde data showed biases within 5 DU and RMS errors less than 10 DU. Comparisons with tropospheric ozone columns derived from limb–nadir matching showed that the bias and RMS are within the range of the CCD_IUP comparison with the sondes.

Description: Comparison of aerosol properties retrieved using GARRLiC, LIRIC, and Raman algorithms applied to multi-wavelength lidar and sun/sky-photometer data Valentyn Bovchaliuk, Philippe Goloub, Thierry Podvin, Igor Veselovskii, Didier Tanre, Anatoli Chaikovsky, Oleg Dubovik, Augustin Mortier, Anton Lopatin, Mikhail Korenskiy, and Stephane Victori Atmos. Meas. Tech., 9, 3391-3405, doi:10.5194/amt-9-3391-2016, 2016 Aerosol particles are important and highly variable components of the terrestrial atmosphere, and they affect both air quality and climate. In order to evaluate their multiple impacts, the most important requirement is to precisely measure their characteristics. Remote sensing technologies such as lidar (light detection and ranging) and sun/sky photometers are powerful tools for determining aerosol optical and microphysical properties. In our work, we applied several methods to joint or separate lidar and sun/sky-photometer data to retrieve aerosol properties. The Raman technique and inversion with regularization use only lidar data. The LIRIC (LIdar-Radiometer Inversion Code) and recently developed GARRLiC (Generalized Aerosol Retrieval from Radiometer and Lidar Combined data) inversion methods use joint lidar and sun/sky-photometer data. This paper presents a comparison and discussion of aerosol optical properties (extinction coefficient profiles and lidar ratios) and microphysical properties (volume concentrations, complex refractive index values, and effective radius values) retrieved using the aforementioned methods. The comparison showed inconsistencies in the retrieved lidar ratios. However, other aerosol properties were found to be generally in close agreement with the AERONET (AErosol RObotic NETwork) products. In future studies, more cases should be analysed in order to clearly define the peculiarities in our results.

Description: Characterisation and improvement of j (O 1 D) filter radiometers Birger Bohn, Dwayne E. Heard, Nikolaos Mihalopoulos, Christian Plass-Dülmer, Rainer Schmitt, and Lisa K. Whalley Atmos. Meas. Tech., 9, 3455-3466, doi:10.5194/amt-9-3455-2016, 2016 Filter radiometers are instruments that quantify the rate of formation of excited oxygen atoms from photolysis of ozone in the atmosphere. The excited oxygen atoms are important for the atmospheric self-cleaning ability. The radiometers were characterised by measurements of their spectral response. Together with field comparisons with a reference instrument, the characterisations improved the performance. That will help to better understand atmospheric photochemistry in future research.

Description: Using paraxial approximation to describe the optical setup of a typical EARLINET lidar system Panagiotis Kokkalis Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2016-230,2016 Manuscript under review for AMT (discussion: open, 0 comments) The mathematical formulation for the optical setup of a typical EARLINET lidar system is given here. The equations describing a lidar system from the emitted laser beam to its projection on the final receiving unit are revealed, based on paraxial approximation and geometric optics approach. The evaluation of the formulation is performed with ray tracing simulations, revealing an overall good performance with relative differences of the order of 5 % mainly attributed to aberrations that are not taken into account in paraxial approximation.

Description: Performance of post-processing algorithms for rainfall intensity measurements of tipping-bucket rain gauges Mattia Stagnaro, Matteo Colli, Luca Giovanni Lanza, and Pak Wai Chan Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2016-257,2016 Manuscript under review for AMT (discussion: open, 0 comments) The research presented in this work involves field data analysis, numerical modelling techniques and approaches to a long-standing problem of liquid precipitation measurements: the sampling and the interpretation of the tipping bucket sensors signal. The present study shows relevant implications of the adopted data processing methods on the accuracy of the rainfall intensity measurements provided by traditional tipping bucket gauges.

Description: GFIT2: an experimental algorithm for vertical profile retrieval from near-IR spectra Brian J. Connor, Vanessa Sherlock, Geoff Toon, Debra Wunch, and Paul O. Wennberg Atmos. Meas. Tech., 9, 3513-3525, doi:10.5194/amt-9-3513-2016, 2016 An algorithm for retrieval of vertical profiles of CO 2 from ground-based spectra is described. Retrieval of CO 2 vertical profiles from would be very beneficial for carbon cycle studies and the validation of satellite measurements. There are approximately 3 degrees of freedom for the CO 2 profile. The accuracy of retrievals of CO 2 from the spectral band used is limited by small errors in the calculated spectrum. Ongoing research is needed and described.

Description: How big is an OMI pixel? Martin de Graaf, Holger Sihler, Lieuwe G. Tilstra, and Piet Stammes Atmos. Meas. Tech., 9, 3607-3618, doi:10.5194/amt-9-3607-2016, 2016 The shapes and sizes of the FoV from the OMI satellite instrument were determined with extensive lab tests but never verified after launch. Here, collocated measurements from MODIS, flying in formation, were used to find the most optimal shape of the OMI FoV. This shape is not quadrangular, as suggested by the provided corner coordinates of a pixel, but rather super-Gaussian shaped and overlapping with the FoV of neighbouring pixels.

Description: A strategy for the measurement of the CO 2 distribution in the stratosphere Massimo Carlotti, Bianca Maria Dinelli, Giada Innocenti, and Luca Palchetti Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2016-220,2016 Manuscript under review for AMT (discussion: open, 0 comments) We introduce a strategy for the measurement of CO 2 in the stratosphere. We use an orbiting limb sounder to measure both the Thermal InfraRed (TIR) and Far-InfraRed (FIR) atmospheric emission. The rotational transitions of O 2 in the FIR are exploited to derive the temperature and pressure fields that are needed to retrieve the CO 2 from its spectrum in the TIR. The proposed experiment can determine two-dimensional distributions of the CO 2 with accuracy of 1 ppm at altitudes between 10 and 50 km.

Description: Smithsonian Astrophysical Observatory Ozone Mapping and Profiler Suite (SAO OMPS) formaldehyde retrieval Gonzalo González Abad, Alexander Vasilkov, Colin Seftor, Xiong Liu, and Kelly Chance Atmos. Meas. Tech., 9, 2797-2812, doi:10.5194/amt-9-2797-2016, 2016 The multi-spectral possibilities of the OMPS Nadir Mapper instrument are exploited here to perform formaldehyde retrievals. Orbiting the Earth at 824 km, OMPS observes the atmosphere in a time frame similar to instruments belonging to NASA's A-Train constellation, 01:30. We show that OMPS is well suited to measure formaldehyde despite its spectral resolution of 1nm. The comparison of OMPS retrievals with OMI products show good temporal correlation.

Description: Accomplishments of the MUSICA project to provide accurate, long-term, global and high-resolution observations of tropospheric {H 2 O, δ D} pairs – a review Matthias Schneider, Andreas Wiegele, Sabine Barthlott, Yenny González, Emanuel Christner, Christoph Dyroff, Omaira E. García, Frank Hase, Thomas Blumenstock, Eliezer Sepúlveda, Gizaw Mengistu Tsidu, Samuel Takele Kenea, Sergio Rodríguez, and Javier Andrey Atmos. Meas. Tech., 9, 2845-2875, doi:10.5194/amt-9-2845-2016, 2016 Tropospheric {H 2 O, δ D} pairs can be observed by remote sensing techniques, but the data quality strongly depends on a comprehensive consideration of the complex nature and a careful calibration of the remote sensing data pairs. This paper reviews the quality assurance/documentation activities of the MUSICA project and demonstrates that MUSICA’s ground-based FTIR and space-based IASI {H 2 O, δ D} pair products are accurate and can be generated at a global scale with high resolution and for long periods.

Description: Top-of-the-atmosphere shortwave flux estimation from satellite observations: an empirical neural network approach applied with data from the A-train constellation Pawan Gupta, Joanna Joiner, Alexander Vasilkov, and Pawan K. Bhartia Atmos. Meas. Tech., 9, 2813-2826, doi:10.5194/amt-9-2813-2016, 2016 The A-train constellation of satellites provides a unique opportunity to analyze near-simultaneous data from several of these sensors. In this paper, retrievals of cloud/aerosols parameters and total column ozone (TCO) from the Aura Ozone Monitoring Instrument (OMI) have been used to develop a variety of neural networks that estimate TOA SWF globally over ocean and land using only OMI data as inputs. Application of our method to other ultraviolet sensors may provide unique estimates of TOA SWF.

Description: Measurement of OH reactivity by laser flash photolysis coupled with laser-induced fluorescence spectroscopy Daniel Stone, Lisa K. Whalley, Trevor Ingham, Peter M. Edwards, Danny R. Cryer, Charlotte A. Brumby, Paul W. Seakins, and Dwayne E. Heard Atmos. Meas. Tech., 9, 2827-2844, doi:10.5194/amt-9-2827-2016, 2016 OH reactivity is the total pseudo-first-order loss rate coefficient describing the removal of OH radicals to all sinks in the atmosphere. Measurements of ambient OH reactivity can be used to discover the extent to which measured OH sinks contribute to the total OH loss rate. In this work, we describe the design and characterisation of an instrument to measure OH reactivity using laser flash photolysis coupled to laser-induced fluorescence (LFP-LIF) spectroscopy.

Description: Improvement of Vertical Velocity Statistics Measured by a Doppler Lidar through Comparison with Sonic Anemometer Observations Timothy A. Bonin, Jennifer F. Newman, Petra M. Klein, Phillip B. Chilson, and Sonia Wharton Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2016-134,2016 Manuscript under review for AMT (discussion: open, 0 comments) Turbulence measurements are important to boundary layer meteorology and related fields. Doppler lidars are capable of providing continuous profiles of turbulence statistics. Herein, the most direct turbulence measurement, vertical velocity variance, is validated with those from sonic anemometers. Spectra are also compared. A method to improve calculated velocity variance using the autocovariance is shown to improve the accuracy of the measurement by mitigating effects of noise and averaging.