http://www.atmos-meas-tech-discuss.net/ Atmospheric Measurement Techniques Discussions Latest Articlesenhttp://www.atmos-meas-tech-discuss.net/5/1075/2012/<b>Temperature profiles with bi-static Doppler-RASS and their accuracy</b><br /><br />Atmospheric Measurement Techniques Discussions, 5, 1075-1100, 2012<br /><br />Author(s): B. Hennemuth, G. Peters, and H.-J. Kirtzel<br /><br />The technique of atmospheric temperature profiling by Doppler-RASS is discussed. The set up with bi-static (separated transmit and receiving) antennas implies a range dependent scattering angle. The retrieval scheme developed by Kon for such antenna geometry is reviewed and its limits of validity are discussed. Empirical tuning of the efficient antenna aperture is proposed to fit the retrieved temperature profiles to reality. Examples of application of the measuring technique for atmospheric boundary layer characterization are presented.Fri, 03 Feb 2012 00:00:00 +0100http://www.atmos-meas-tech-discuss.net/5/1029/2012/<b>SCIAMACHY lunar occultation water vapor measurements: retrieval and validation results</b><br /><br />Atmospheric Measurement Techniques Discussions, 5, 1029-1073, 2012<br /><br />Author(s): F. Azam, K. Bramstedt, A. Rozanov, K. Weigel, H. Bovensmann, G. P. Stiller, and J. P. Burrows<br /><br />SCIAMACHY lunar occultation measurements have been used to derive vertical profiles of stratospheric water vapor for the Southern Hemisphere in the near infrared (NIR) spectral range of 1350–1420 nm. The focus of this study is to present the retrieval methodology including the sensitivity studies and optimizations for the implementation of the radiative transfer model on SCIAMACHY lunar occultation measurements. The study also includes the validation of the data product with the collocated measurements from two satellite occultation instruments and two instruments measuring in limb geometry. The SCIAMACHY lunar occultation water vapor measurements comparisons with the ACE-FTS instrument have shown an agreement of 5% on the average that is well within the reported biases of ACE in the stratosphere. The comparisons with HALOE have also shown good results where the agreement between the instruments is within 5%. The validations of the lunar occultation water vapor measurements with MLS instrument are exceptionally good varying between 1.5 to around 4%. The validations with MIPAS are in the range of 10%. A validated dataset of water vapor vertical distributions from SCIAMACHY lunar occultation measurements is expected to facilitate the understanding of physical and chemical processes in the southern mid-latitudes and the dynamical processes related to polar vortex.Fri, 03 Feb 2012 00:00:00 +0100http://www.atmos-meas-tech-discuss.net/5/1003/2012/<b>A new algorithm for brown and black carbon identification and organic carbon detection in fine atmospheric aerosols by a multi-wavelength Aethalometer</b><br /><br />Atmospheric Measurement Techniques Discussions, 5, 1003-1027, 2012<br /><br />Author(s): F. Esposito, M. R. Calvello, E. Gueguen, and G. Pavese<br /><br />A novel approach for the analysis of aerosol absorption coefficient measurements is presented. A 7-wavelenghts aethalometer has been employed to identify brown carbon (BrC) and black carbon (BC) and to detect organic carbon (OC) in fine atmospheric aerosols (PM_2.5). The Magee Aethalometer estimates the BC content in atmospheric particulate by measuring the light attenuation in the aerosols accumulated on a quartz filter, at the standard wavelength &lambda; = 0.88 μm. The known Magee algorithm is based on the hypothesis of a mass absorption coefficient inversely proportional to the wavelength. The new algorithm has been developed and applied to the whole spectral range; it verifies the spectral absorption behavior and, thus, it distinguishes between black and brown carbon. Moreover, it allows also to correct the absorption estimation at the UV wavelength commonly used to qualitatively detect the presence of mixed hydrocarbons. The algorithm has been applied to data collected in Agri Valley, located in Southern Italy, where torched crude oil undergoes a pre-treatment process. <br><br> The Magee Aethalometer has been set to measure Aerosol absorption coefficients &tau;_aer (&lambda;, <i>t</i>) every 5 min. Wavelength dependence of &tau;_aer (&lambda;, <i>t</i>) has been analyzed by a best-fit technique and, excluding UV-wavelengths, both the absorption Angstrom coefficient &alpha; and the BC (or BrC) concentration have been determined. Finally, daily histograms of &alpha; provide information on optical properties of carbonaceous aerosol, while the extrapolation at UV-wavelengths gives information on the presence of semivolatile organic carbon (OC) particles.Wed, 01 Feb 2012 00:00:00 +0100http://www.atmos-meas-tech-discuss.net/5/979/2012/<b>Improved retrieval of SO₂ from Ozone Monitoring Instrument: residual analysis and data noise correction</b><br /><br />Atmospheric Measurement Techniques Discussions, 5, 979-1001, 2012<br /><br />Author(s): H. Yan, L. Chen, J. Tao, L. Su, and D. Han<br /><br />In this study, based on Ozone Monitoring Instrument (OMI) observation data and considering the shortage of current Band Residual Difference algorithm (BRD) algorithm in data noise correction since late 2008, we make a detailed analysis of OMI SO₂ main noise sources and determine the best residual adjustment area by analyzing the different residual correction effects. After such modification, the OMI SO₂ PBL results noise which use BRD retrieval algorithm is largely reduced, the precision of the SO₂ results is improved, and the optimization of the BRD algorithm for data noise is realized. We select China as our study area and compare the results between the optimized results and the OMI SO₂ PBL products. Results show that they are consistent with each other in January 2008; however, our modified algorithm results have higher precision and more reliable SO₂ spatial distribution in January 2009. Finally, other current retrieval error sources are discussed, and further research is needed on these areas.Fri, 27 Jan 2012 00:00:00 +0100http://www.atmos-meas-tech-discuss.net/5/947/2012/<b>A gas chromatographic instrument for measurement of hydrogen cyanide in the lower atmosphere</b><br /><br />Atmospheric Measurement Techniques Discussions, 5, 947-978, 2012<br /><br />Author(s): J. L. Ambrose, Y. Zhou, K. Haase, H. R. Mayne, R. Talbot, and B. C. Sive<br /><br />A gas-chromatographic (GC) instrument was developed for measuring hydrogen cyanide (HCN) in the lower atmosphere. The main features of the instrument are (1) a cryogen-free cooler for sample dehumidification and enrichment, (2) a porous polymer PLOT column for analyte separation, (3) a flame thermionic detector (FTD) for sensitive and selective detection and (4) a dynamic dilution system for calibration. We deployed the instrument for a ~4 month period from January&ndash;June 2010 at the AIRMAP atmospheric monitoring station Thompson Farm 2 (THF2) in rural Durham, NH. A subset of measurements made during 3&ndash;31 March is presented here with a detailed description of the instrument features and performance characteristics. The temporal resolution of the measurements was ~20 min, with a 75 s sample capture time. The 1&sigma; measurement precision was <10% and the instrument response linearity was excellent on a calibration scale of 0.10&ndash;0.75 ppbv (&plusmn;5%). The estimated method detection limit (MDL) and accuracy were 0.021 ppbv and 15%, respectively. From 3&ndash;31 March 2010, ambient HCN mixing ratios ranged from 0.15&ndash;1.0 ppbv (&plusmn;15%), with a mean value of 0.36 &plusmn; 0.16 ppbv (1&sigma;). The approximate mean background HCN mixing ratio of 0.20 &plusmn; 0.04 ppbv appeared to agree well with tropospheric column measurements reported previously. The GC-FTD HCN measurements were strongly correlated with acetonitrile (CH₃CN) measured concurrently with a proton transfer-reaction mass spectrometer (PTR-MS), as anticipated given our understanding that the nitriles share a common primary biomass burning source to the global atmosphere. The nitriles were overall only weakly correlated with CO, which is reasonable considering the greater diversity of sources for CO. However, strong correlations with CO were observed on several nights under stable atmospheric conditions and suggest regional combustion-based sources for the nitriles. These results demonstrate that the GC-FTD instrument is capable of making long term, in-situ measurements of HCN in the lower atmosphere. To date, similar measurements have not been performed, yet they are critically needed to (1) better evaluate the regional scale distribution of HCN in the atmosphere and (2) discern the influence of biomass burning on surface air composition in remote regions.Fri, 27 Jan 2012 00:00:00 +0100http://www.atmos-meas-tech-discuss.net/5/909/2012/<b>Multi-sensor Aerosol Products Sampling System (MAPSS)</b><br /><br />Atmospheric Measurement Techniques Discussions, 5, 909-945, 2012<br /><br />Author(s): M. Petrenko, C. Ichoku, and G. Leptoukh<br /><br />Global and local properties of atmospheric aerosols have been extensively observed and measured using both spaceborne and ground-based instruments, especially during the last decade. Unique properties retrieved by the different instruments contribute to an unprecedented availability of the most complete set of complimentary aerosol measurements ever acquired. However, some of these measurements remain underutilized, largely due to the complexities involved in analyzing them synergistically. To characterize the inconsistencies and bridge the gap that exists between the sensors, we have established a Multi-sensor Aerosol Products Sampling System (MAPSS), which consistently samples and generates the spatial statistics (mean, standard deviation, direction and rate of spatial variation, and spatial correlation coefficient) of aerosol products from multiple spaceborne sensors, including MODIS (on Terra and Aqua), MISR, OMI, POLDER, CALIOP, and SeaWiFS. Samples of satellite aerosol products are extracted over Aerosol Robotic Network (AERONET) locations as well as over other locations of interest such as those with available ground-based aerosol observations. In this way, MAPSS enables a direct cross-characterization and data integration between Level-2 aerosol observations from multiple sensors. In addition, the available well-characterized co-located ground-based data provides the basis for the integrated validation of these products. This paper explains the sampling methodology and concepts used in MAPSS, and demonstrates specific examples of using MAPSS for an integrated analysis of multiple aerosol products.Thu, 26 Jan 2012 00:00:00 +0100http://www.atmos-meas-tech-discuss.net/5/881/2012/<b>Multiple scattering in a dense aerosol atmosphere</b><br /><br />Atmospheric Measurement Techniques Discussions, 5, 881-907, 2012<br /><br />Author(s): S. Mukai, T. Yokomae, I. Sano, M. Nakata, and A. Kokhanovsky<br /><br />This study was designed to develop an efficient algorithm to retrieve aerosol characteristics in aerosol events, which are associated with dense concentrations of aerosols in the atmosphere, such as a dust storm or a biomass burning plume. The idea of successive scattering of light is reviewed based on the theory of radiative transfer. Then derivation of the method of successive order of scattering (MSOS) is interpreted in detail, and it is shown that MSOS is available for a simulation scheme in the dense radiation field being used to retrieve aerosol properties in the event with the high optical thickness. Finally our algorithms are practically applied for the biomass burning aerosol event over the Amazon using Aqua/MODIS data.Tue, 24 Jan 2012 00:00:00 +0100http://www.atmos-meas-tech-discuss.net/5/839/2012/<b>On the accuracy of integrated water vapor observations and the potential for mitigating electromagnetic path delay error in InSAR</b><br /><br />Atmospheric Measurement Techniques Discussions, 5, 839-880, 2012<br /><br />Author(s): D. Cimini, N. Pierdicca, E. Pichelli, R. Ferretti, V. Mattioli, S. Bonafoni, M. Montopoli, and D. Perissin<br /><br />A field campaign was carried out in the framework of the Mitigation of Electromagnetic Transmission errors induced by Atmospheric Water Vapour Effects (METAWAVE) project sponsored by the European Space Agency (ESA) to investigate the accuracy of currently available sources of atmospheric columnar integrated water vapor measurements. The METAWAVE campaign took place in Rome, Italy, for the 2-week period from 19 September to 4 October 2008. The collected dataset includes observations from ground-based microwave radiometers and Global Positioning System (GPS) receivers, from meteorological numerical model analysis and predictions, from balloon-borne in-situ radiosoundings, as well as from spaceborne infrared radiometers. These different sources of integrated water vapor (IWV) observations have been analyzed and compared to quantify the accuracy and investigate the potential for mitigating IWV-related electromagnetic path delay errors in Interferometric Synthetic Aperture Radar (InSAR) imaging. The results, which include a triple collocation analysis accounting for errors inherently present in every IWV measurements, are valid not only to InSAR but also to any other application involving water vapor sensing. The present analysis concludes that the sensitivity of InSAR to water vapor turbulent component is significantly higher than that of the other instruments analyzed here. Nonetheless, information on the IWV vertical stratification from satellite observations, numerical models, and GPS receivers may provide valuable aid to suppress the long spatial wavelength (>20 km) component of the atmospheric delay, and thus significantly improve the performances of InSAR phase unwrapping techniques.Tue, 24 Jan 2012 00:00:00 +0100http://www.atmos-meas-tech-discuss.net/5/813/2012/<b>Site selective real-time measurements of atmospheric N₂O isotopomers by laser spectroscopy</b><br /><br />Atmospheric Measurement Techniques Discussions, 5, 813-838, 2012<br /><br />Author(s): J. Mohn, B. Tuzson, A. Manninen, N. Yoshida, S. Toyoda, W. A. Brand, and L. Emmenegger<br /><br />We describe the first high precision real-time analysis of the N₂O site-specific isotopic composition at ambient mixing ratios. Our technique is based on mid-infrared quantum cascade laser absorption spectroscopy (QCLAS) combined with an automated preconcentration unit. The QCLAS allows for simultaneous and specific analysis of the three main stable N₂O isotopic species, ¹⁴N¹⁵N¹⁶O, ¹⁵N¹⁴N¹⁶O, ¹⁴N¹⁴N¹⁶O, and the respective site-specific relative isotope ratio differences &delta;¹⁵N^&alpha; and &delta;¹⁵N^&beta;. Continuous, stand-alone operation is achieved by using liquid nitrogen free N₂O preconcentration, a quasi-room-temperature quantum cascade laser (QCL), quantitative sample transfer to the QCLAS, and an optimized calibration algorithm. The N₂O site-specific isotopic composition (&delta;¹⁵N^&alpha; and &delta;¹⁵N^&beta;) can be analysed with a long term precision of 0.2&permil;. The potential of this analytical tool is illustrated by continuous N₂O isotopomer measurements above a grassland plot over three weeks period, which allowed identification of microbial source and sink processes.Mon, 23 Jan 2012 00:00:00 +0100http://www.atmos-meas-tech-discuss.net/5/775/2012/<b>New dynamic NNORSY ozone profile climatology</b><br /><br />Atmospheric Measurement Techniques Discussions, 5, 775-812, 2012<br /><br />Author(s): A. K. Kaifel, M. Felder, C. DeClercq, and J.-C. Lambert<br /><br />Climatological ozone profile data are widely used as a-priori information for total ozone using DOAS type retrievals as well as for ozone profile retrieval using optimal estimation, for data assimilation or evaluation of 3-D chemistry-transport models and a lot of other applications in atmospheric sciences and remote sensing. For most applications it is important that the climatology represents not only long term mean values but also the links between ozone and dynamic input parameters. These dynamic input parameters should be easily accessible from auxiliary datasets or easily measureable, and obviously should have a high correlation with ozone. For ozone profile these parameters are mainly total ozone column and temperature profile data. This was the outcome of a user consultation carried out in the framework of developing a new, dynamic ozone profile climatology. <br><br> The new ozone profile climatology is based on the Neural Network Ozone Retrieval System (NNORSY) widely used for ozone profile retrieval from UV and IR satellite sounder data. NNORSY allows implicit modelling of any non-linear correspondence between input parameters (predictors) and ozone profile target vector. This paper presents the approach, setup and validation of a new family of ozone profile climatologies with static as well as dynamic input parameters (total ozone and temperature profile). The neural network training relies on ozone profile measurement data of well known quality provided by ground based (ozonesondes) and satellite based (SAGE II, HALOE, and POAM-III) measurements over the years 1995–2007. In total, four different combinations (modes) for input parameters (date, geolocation, total ozone column and temperature profile) are available. <br><br> The geophysical validation spans from pole to pole using independent ozonesonde, lidar and satellite data (ACE-FTS, AURA-MLS) for individual and time series comparisons as well as for analysing the vertical and meridian structure of different modes of the NNORSY ozone profile climatology. The NNORSY ozone profile climatology is available to the community as a comprehensive software library.Wed, 18 Jan 2012 00:00:00 +0100http://www.atmos-meas-tech-discuss.net/5/747/2012/<b>Evaluation of turbulent dissipation rate retrievals from Doppler cloud radar</b><br /><br />Atmospheric Measurement Techniques Discussions, 5, 747-774, 2012<br /><br />Author(s): M. D. Shupe, I. M. Brooks, and G. Canut<br /><br />Turbulent dissipation rate retrievals from cloud radar Doppler velocity measurements are evaluated using independent, in situ observations in Arctic stratocumulus clouds. In situ validation data sets of dissipation rate are derived using sonic anemometer measurements from a tethered balloon and high frequency pressure variation observations from a research aircraft, both flown in proximity to stationary, ground-based radars. Modest biases are found among the data sets in particularly low- or high-turbulence regimes, but in general the radar-retrieved values correspond well with the in situ measurements. Root mean square differences are typically a factor of 4–6 relative to any given magnitude of dissipation rate. These differences are no larger than those found when comparing dissipation rates computed from tethered-balloon and 15-m tower sonic measurements made at spatial distances of a few hundred meters. Moreover, radar retrievals are able to capture the vertical dissipation rate structure observed by the in situ sensors, while offering substantially more information on the time variability of turbulence profiles. Together these evaluations indicate that radar-based retrievals can, at a minimum, be used to determine the vertical structure of turbulence in Arctic stratocumulus clouds.Wed, 18 Jan 2012 00:00:00 +0100http://www.atmos-meas-tech-discuss.net/5/691/2012/<b>Desert dust satellite retrieval intercomparison</b><br /><br />Atmospheric Measurement Techniques Discussions, 5, 691-746, 2012<br /><br />Author(s): E. Carboni, G. E. Thomas, A. M. Sayer, R. Siddans, C. A. Poulsen, R. G. Grainger, C. Ahn, D. Antoine, S. Bevan, R. Braak, H. Brindley, S. DeSouza-Machado, J. L. Deuzé, D. Diner, F. Ducos, W. Grey, C. Hsu, O. V. Kalashnikova, R. Kahn, P. R. J. North, C. Salustro, A. Smith, D. Tanré, O. Torres, and B. Veihelmann<br /><br />This work provides a comparison of satellite retrievals of Saharan desert dust aerosol optical depth (AOD) during a strong dust event through March 2006. In this event, a large dust plume was transported over desert, vegetated, and ocean surfaces. The aim is to identify and understand the differences between current algorithms, and hence improve future retrieval algorithms. The satellite instruments considered are AATSR, AIRS, MERIS, MISR, MODIS, OMI, POLDER, and SEVIRI. An interesting aspect is that the different algorithms make use of different instrument characteristics to obtain retrievals over bright surfaces. These include multi-angle approaches (MISR, AATSR), polarisation measurements (POLDER), single-view approaches using solar wavelengths (OMI, MODIS), and the thermal infrared spectral region (SEVIRI, AIRS). Differences between instruments, together with the comparison of different retrieval algorithms applied to measurements from the same instrument, provide a unique insight into the performance and characteristics of the various techniques employed. As well as the intercomparison between different satellite products, the AODs have also been compared to co-located AERONET data. Despite the fact that the agreement between satellite and AERONET AODs is reasonably good for all of the datasets, there are significant differences between them when compared to each other, especially over land. These differences are partially due to differences in the algorithms, such as assumptions about aerosol model and surface properties. However, in this comparison of spatially and temporally averaged data, at least as significant as these differences are sampling issues related to the actual footprint of each instrument on the heterogeneous aerosol field, cloud identification and the quality control flags of each dataset.Tue, 17 Jan 2012 00:00:00 +0100http://www.atmos-meas-tech-discuss.net/5/663/2012/<b>Sensitivity of the Single Particle Soot Photometer to different black carbon types</b><br /><br />Atmospheric Measurement Techniques Discussions, 5, 663-690, 2012<br /><br />Author(s): M. Laborde, P. Mertes, P. Zieger, J. Dommen, U. Baltensperger, and M. Gysel<br /><br />Black carbon (BC) is nowadays mainly of anthropogenic origin. It is the dominant light absorbing component of atmospheric aerosols, playing an important role in the earth's radiative balance and therefore relevant to climate change studies. In addition, BC is known to be harmful to humans making it relevant to policy makers. Nevertheless, the measurement of BC remains biased by the instrument-based definition of BC. The Single Particle Soot Photometer (SP2), allows the measurement of the refractory BC (rBC) mass of individual particle using laser-induced incandescence. However the SP2 needs an empirical calibration to retrieve the rBC mass from the incandescence signal and the sensitivity of the SP2 differs between different BC types. Ideally, for atmospheric studies, the SP2 should be calibrated using ambient particles containing a known mass of ambient rBC. However, such "ambient BC" calibration particles cannot easily be obtained and thus commercially available BC particles are commonly used for SP2 calibration instead. In this study we tested the sensitivity of the SP2 to different BC types in order to characterize the potential error introduced by using non-ambient BC for calibration. The sensitivity of the SP2 was determined for rBC from thermodenuded diesel exhaust, wood burning exhaust and ambient particles as well as for commercially available products: Aquadag^® and fullerene soot. <br><br> Thermodenuded, fresh diesel exhaust has been found to be ideal for SP2 calibration for two reasons. First, the small amount of non-BC matter upon emission reduces the risk of bias due to incomplete removal of non-BC matter and second, it is considered to represent atmospheric rBC as diesel exhaust is the main source of BC in most locations. The SP2 was found to be up to 16% less sensitive to rBC from thermodenuded ambient particles (&le;15 fg) than rBC from diesel exhaust, however, at least part of this difference can be explained by incomplete removal of non-refractory components in the thermodenuder. The SP2 sensitivity to rBC from wood burning exhaust agrees with the one of rBC from diesel exhaust within an error of less than 14% (&le;40 fg). <br><br> If, due to experimental restrictions, diesel exhaust cannot be used, untreated fullerene soot was found to give a SP2 calibration curve similar to diesel exhaust and ambient rBC (within ±10% for a rBC mass &le;15 fg) and is therefore recommended although two different batches differed by ~14% between themselves. In addition, the SP2 was found to be up to 40% more sensitive to Aquadag^® than to diesel exhaust rBC. Therefore Aquadag^® cannot be recommended for atmospheric application. These findings for fullerene soot and Aquadag^®confirm results from previous literature.Tue, 17 Jan 2012 00:00:00 +0100http://www.atmos-meas-tech-discuss.net/5/627/2012/<b>Retrieving aerosol in a cloudy environment: aerosol availability as a function of spatial and temporal resolution</b><br /><br />Atmospheric Measurement Techniques Discussions, 5, 627-662, 2012<br /><br />Author(s): L. A. Remer, S. Mattoo, R. C. Levy, A. Heidinger, R. B. Pierce, and M. Chin<br /><br />The challenge of using satellite observations to retrieve aerosol properties in a cloudy environment is to prevent contamination of the aerosol signal from clouds, while maintaining sufficient aerosol product yield to satisfy specific applications. We investigate aerosol retrieval availability at different instrument pixel resolutions, using the standard MODIS aerosol cloud mask applied to MODIS data and a new GOES-R cloud mask applied to GOES data for a domain covering North America and surrounding oceans. Aerosol availability is not the same as the cloud free fraction and takes into account the technqiues used in the MODIS algorithm to avoid clouds, reduce noise and maintain sufficient numbers of aerosol retrievals. The inherent spatial resolution of each instrument, 0.5 × 0.5 km for MODIS and 1 × 1 km for GOES, is systematically degraded to 1 × 1 km, 2 × 2 km, 4 × 4 km and 8 × 8 km resolutions and then analyzed as to how that degradation would affect the availability of an aerosol retrieval, assuming an aerosol product resolution at 8 × 8 km. The results show that as pixel size increases, availability decreases until at 8 × 8 km 70% to 85% of the retrievals available at 0.5 km have been lost. The diurnal pattern of aerosol retrieval availability examined for one day in the summer suggests that coarse resolution sensors (i.e. 4 × 4 km or 8 × 8 km) may be able to retrieve aerosol early in the morning that would otherwise be missed at the time of current polar orbiting satellites, but not the diurnal aerosol properties due to cloud cover developed during the day. In contrast finer resolution sensors (i.e. 1 × 1 km or 2 × 2 km) have much better opportunity to retrieve aerosols in the partly cloudy scenes and better chance of returning the diurnal aerosol properties. Large differences in the results of the two cloud masks designed for MODIS aerosol and GOES cloud products strongly reinforce that cloud masks must be developed with specific purposes in mind and that a generic cloud mask applied to an independent aerosol retrieval will likely fail.Fri, 13 Jan 2012 00:00:00 +0100http://www.atmos-meas-tech-discuss.net/5/589/2012/<b>Multi-wavelength Raman lidar, sunphotometric and aircraft measurements in combination with inversion models for the estimation of the aerosol optical and physico-chemical properties over Athens, Greece</b><br /><br />Atmospheric Measurement Techniques Discussions, 5, 589-625, 2012<br /><br />Author(s): R. E. Mamouri, A. Papayannis, V. Amiridis, D. Müller, P. Kokkalis, S. Rapsomanikis, E. T. Karageorgos, G. Tsaknakis, A. Nenes, S. Kazadzis, and E. Remoundaki<br /><br />A novel procedure has been developed to retrieve, simultaneously, the optical, microphysical and chemical properties of tropospheric aerosols with a multi-wavelength Raman lidar system in the troposphere over an urban site (Athens, Greece: 37.9° N, 23.6° E, 200 m a.s.l.) using data obtained during the European Space Agency (ESA) THERMOPOLIS project which took place between 15–31 July 2009 over the Greater Athens Area (GAA). We selected to apply our procedure for a case study of intense aerosol layers occurred on 20–21 July 2009. The National Technical University of Athens (NTUA) EOLE 6-wavelength Raman lidar system has been used to provide the vertical profiles of the optical properties of aerosols (extinction and backscatter coefficients, lidar ratio) and the water vapor mixing ratio. An inversion algorithm was used to derive the mean aerosol microphysical properties (mean effective radius – <i>r</i>_eff), single-scattering albedo (ω) and mean complex refractive index (<i>m</i>) at selected heights in the 2–3 km height region. We found that <i>r</i>_eff was 0.3–0.4 μm, ω at 532 nm ranged from 0.63 to 0.88 and <i>m</i> ranged from 1.45 + 0.015<i>i</i> to 1.56 + 0.05<i>i</i>, in good accordance with in situ aircraft measurements. The final data set of the aerosol microphysical properties along with the water vapor and temperature profiles were incorporated into the ISORROPIA model to infer an in situ aerosol composition consistent with the retrieved <i>m</i> and ω values. The retrieved aerosol chemical composition in the 2–3 km height region gave a variable range of sulfate (0–60%) and organic carbon (OC) content (0–50%), although the OC content increased (up to 50%) and the sulfate content dropped (up to 30%) around 3 km height; in connection with the retrieved low ω value (0.63), indicates the presence of absorbing biomass burning smoke mixed with urban haze. Finally, the retrieved aerosol microphysical properties were compared with column-integrated sunphotometer data.Fri, 13 Jan 2012 00:00:00 +0100http://www.atmos-meas-tech-discuss.net/5/517/2012/<b>Validation of ACE and OSIRIS ozone and NO₂ measurements using ground-based instruments at 80° N</b><br /><br />Atmospheric Measurement Techniques Discussions, 5, 517-588, 2012<br /><br />Author(s): C. Adams, K. Strong, R. L. Batchelor, P. F. Bernath, S. Brohede, C. Boone, D. Degenstein, W. H. Daffer, J. R. Drummond, P. F. Fogal, E. Farahani, C. Fayt, A. Fraser, F. Goutail, F. Hendrick, F. Kolonjari, R. Lindenmaier, G. Manney, C. T. McElroy, C. A. McLinden, J. Mendonca, J.-H. Park, B. Pavlovic, A. Pazmino, C. Roth, V. Savastiouk, K. A. Walker, D. Weaver, and X. Zhao<br /><br />The Optical Spectrograph and Infra-Red Imager System (OSIRIS) and the Atmospheric Chemistry Experiment (ACE) have been taking measurements from space since 2001 and 2003, respectively. This paper presents intercomparisons between ozone and NO₂ measured by the ACE and OSIRIS satellite instruments and by ground-based instruments at the Polar Environment Atmospheric Research Laboratory (PEARL), which is located at Eureka, Canada (80° N, 86° W) and is operated by the Canadian Network for the Detection of Atmospheric Change (CANDAC). The ground-based instruments included in this study are four zenith-sky differential optical absorption spectroscopy (DOAS) instruments, one Bruker Fourier transform infrared spectrometer (FTIR) and four Brewer spectrophotometers. Ozone total columns measured by the DOAS instruments were retrieved using new Network for the Detection of Atmospheric Composition Change (NDACC) guidelines and agree to within 3.2%. The DOAS ozone columns agree with the Brewer spectrophotometers with mean relative differences that are smaller than 1.5%. This suggests that for these instruments the new NDACC data guidelines were successful in producing a homogenous and accurate ozone dataset at 80° N. Satellite 14–52 km ozone and 17–40 km NO₂ partial columns within 500 km of PEARL were calculated for ACE-FTS Version 2.2 (v2.2) plus updates, ACE-FTS v3.0, ACE-MAESTRO (Measurements of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation) v1.2 and OSIRIS SaskMART v5.0x ozone and Optimal Estimation v3.0 NO₂ data products. The new ACE-FTS v3.0 and the validated ACE-FTS v2.2 partial columns are nearly identical, with mean relative differences of 0.0 ± 0.2% for ozone and −0.2 ± 0.1% for v2.2 minus v3.3 NO₂. Ozone columns were constructed from 14–52 km satellite and 0–14 km ozonesonde partial columns and compared with the ground-based total column measurements. The satellite-plus-sonde measurements agree with the ground-based ozone total columns with mean relative differences of 0.1–7.3%. For NO₂, partial columns from 17 km upward were scaled to noon using a photochemical model. Mean relative differences between OSIRIS, ACE-FTS and ground-based NO₂ measurements do not exceed 20%. ACE-MAESTRO measures more NO₂ than the other instruments, with mean relative differences of 25–52%. Seasonal variation in the differences between partial columns is observed, suggesting that there are systematic errors in the measurements, the photochemical model corrections, and/or in the coincidence criteria. For ozone spring-time measurements, additional coincidence criteria based on stratospheric temperature and the location of the polar vortex were found to improve agreement between some of the instruments. For ACE-FTS v2.2 minus Bruker FTIR, the 2007–2009 spring-time mean relative difference improved from −5.0 ± 0.4% to −3.1 ± 0.8% with the dynamical selection criteria. This was the largest improvement, likely because both instruments measure direct sunlight and therefore have well-characterized lines-of-sight compared with scattered sunlight measurements. For NO₂, the addition of a ±1° latitude coincidence criterion improved spring-time intercomparison results, likely due to the sharp latitudinal gradient of NO₂ during polar sunrise. The differences between satellite and ground-based measurements do not show any obvious trends over the missions, indicating that both the ACE and OSIRIS instruments continue to perform well.Thu, 12 Jan 2012 00:00:00 +0100http://www.atmos-meas-tech-discuss.net/5/471/2012/<b>Relative drifts and stability of satellite and ground-based stratospheric ozone profiles at NDACC lidar stations</b><br /><br />Atmospheric Measurement Techniques Discussions, 5, 471-516, 2012<br /><br />Author(s): P. J. Nair, S. Godin-Beekmann, L. Froidevaux, L. E. Flynn, J. M. Zawodny, J. M. Russell III, A. Pazmiño, G. Ancellet, W. Steinbrecht, H. Claude, T. Leblanc, S. McDermid, J. A. E. van Gijsel, B. Johnson, A. Thomas, D. Hubert, J.-C. Lambert, and H. Nakane<br /><br />The long-term evolution of stratospheric ozone at different stations in the low and mid-latitudes is investigated. The analysis is performed by comparing the collocated profiles of ozone lidars, at the northern mid-latitudes (Meteorological Observatory Hohenpeißenberg, Haute-Provence Observatory, Tsukuba and Table Mountain Facility), tropics (Mauna Loa Observatory) and southern mid-latitudes (Lauder), with ozonesondes and space-borne sensors (SBUV(/2), SAGE II, HALOE, UARS MLS and Aura MLS), extracted around the stations. Relative differences are calculated to find biases and temporal drifts in the measurements. All measurement techniques show their best agreement with respect to the lidar at 20–40 km, where the differences are within &plusmn;3% and drifts are less than &plusmn;0.3% yr^&minus;1 at all stations. In addition, the stability of the long-term ozone observations (lidar, SBUV(/2), SAGE II and HALOE) is evaluated by the cross-comparison of each data set. In general, all lidars and SBUV(/2) exhibit near zero drifts and the comparison between SAGE II and HALOE shows larger, but insignificant drifts. The RMS of the drifts of lidar and SBUV(/2) is 0.22 and 0.27% yr^&minus;1, respectively. The average drifts of the long-term data sets, derived from various comparisons, are less than &plusmn;0.3% yr^&minus;1 in 20–40 km at all stations. A combined time series of the relative differences between SAGE II, HALOE and Aura MLS with respect to lidar data at six sites is constructed, to obtain long-term data sets lasting up to 27 yr. The relative drifts derived from these combined data are very small, within &plusmn;0.2% yr^&minus;1.Thu, 12 Jan 2012 00:00:00 +0100http://www.atmos-meas-tech-discuss.net/5/447/2012/<b>Using sonic anemometer temperature to measure sensible heat flux in strong winds</b><br /><br />Atmospheric Measurement Techniques Discussions, 5, 447-469, 2012<br /><br />Author(s): S. P. Burns, T. W. Horst, P. D. Blanken, and R. K. Monson<br /><br />The sensible heat flux (<i>H</i>) is a significant component of the surface energy balance (SEB). Sonic anemometers simultaneously measure the turbulent fluctuations of vertical wind (<i>w</i>') and sonic temperature (<i>T</i>_s'), and are commonly used to measure <i>H</i>. Our study examines 30-min heat fluxes measured with a Campbell Scientific model CSAT3 sonic anemometer above a subalpine forest. We compare <i>H</i> calculated with <i>T</i>_s to <i>H</i> calculated with a co-located thermocouple and find that for horizontal wind speed (<i>U</i>) less than 8 m s⁻¹ the agreement is &asymp;&plusmn;30 W m⁻². However, for <i>U</i> &gt;&asymp; 8 m s⁻¹, the CSAT3 <i>H</i> becomes larger than <i>H</i> calculated with the thermocouple, reaching a maximum difference of ≈250 W m⁻² at <i>U</i> ≈ 18 m s⁻¹. <i>H</i> calculated with the thermocouple results in a SEB that is relatively independent of <i>U</i> at high wind speeds. In contrast, the SEB calculated with <i>H</i> from the CSAT3 varies considerably with <i>U</i>, particularly at night. Cospectral analysis of <span style="border-top: 1px solid #000;color:#000;"><i>w</i>'<i>T</i>_s'</span> suggest that spurious correlation is a problem during high winds which leads to a positive (additive) increase in <i>H</i> calculated with the CSAT3. At night, when <i>H</i> is typically negative, this CSAT3 error results in a measured <i>H</i> that falsely approaches zero or even becomes positive. Within a broader context, the usefulness of side-by-side instrument comparisons are discussed.Thu, 12 Jan 2012 00:00:00 +0100http://www.atmos-meas-tech-discuss.net/5/411/2012/<b>Using Markov switching models to infer dry and rainy periods from telecommunication microwave link signals</b><br /><br />Atmospheric Measurement Techniques Discussions, 5, 411-445, 2012<br /><br />Author(s): Z. Wang, M. Schleiss, J. Jaffrain, A. Berne, and J. Rieckermann<br /><br />A Markov switching algorithm is introduced to classify attenuation measurements from telecommunication microwave links into dry and rainy periods. It is based on a simple state-space model and has the advantage of not relying on empirically estimated threshold parameters. The algorithm is applied to data collected using a new and original experimental set-up in the vicinity of Zürich, Switzerland. The false dry and false rain detection rates of the algorithm are evaluated and compared to 3 other algorithms from the literature. The results show that, on average, the Markov switching model outperforms the other algorithms. It is also shown that the classification performance can be further improved if redundant information from multiple channels is used.Thu, 12 Jan 2012 00:00:00 +0100http://www.atmos-meas-tech-discuss.net/5/385/2012/<b>Atmospheric effect on the ground-based measurements of broadband surface albedo</b><br /><br />Atmospheric Measurement Techniques Discussions, 5, 385-409, 2012<br /><br />Author(s): T. Manninen, A. Riihelä, and G. de Leeuw<br /><br />Ground-based pyranometer measurements of broadband surface albedo values are affected by the atmospheric conditions. A new method for estimating the magnitude of this effect in clear sky conditions is presented. Global and reflected radiation values and AOD values at two wavelengths are needed to apply the method. Depending on the atmospheric optical depth and the sun zenith angle values the effect can be as large as 20%. For the test case of Cabauw the atmosphere caused typically 5% higher surface albedo values than the corresponding black-sky surface albedo values.Wed, 11 Jan 2012 00:00:00 +0100