Consistency of aerosols above clouds characterization from A-Train active and passive measurements

• Published in: Atmospheric Measurement Techniques
• Main Authors: L. T. Deaconu, F. Waquet, D. Josset, N. Ferlay, F. Peers, F. Thieuleux, F. Ducos, N. Pascal, D. Tanré, J. Pelon, P. Goloub
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2017
• Subjects: Environmental engineering; TA170-171; Earthwork. Foundations; TA715-787; Pacific; North Atlantic; South Atlantic Ocean
• Online Access: https://doi.org/10.5194/amt-10-3499-2017; https://doaj.org/article/877b92e3e10741d4a9dc588082070c41

This study presents a comparison between the retrieval of optical properties of aerosol above clouds (AAC) from different techniques developed for the A-Train sensors CALIOP/CALIPSO and POLDER/PARASOL. The main objective is to analyse the consistency between the results derived from the active and the passive measurements. We compare the aerosol optical thickness (AOT) above optically thick clouds (cloud optical thickness (COT) larger than 3) and their Ångström exponent (AE). These parameters are retrieved with the CALIOP operational method, the POLDER operational polarization method and the CALIOP-based depolarization ratio method (DRM) – for which we also propose a calibrated version (denominated DRM SODA , where SODA is the Synergized Optical Depth of Aerosols). We analyse 6 months of data over three distinctive regions characterized by different types of aerosols and clouds. Additionally, for these regions, we select three case studies: a biomass-burning event over the South Atlantic Ocean, a Saharan dust case over the North Atlantic Ocean and a Siberian biomass-burning event over the North Pacific Ocean. Four and a half years of data are studied over the entire globe for distinct situations where aerosol and cloud layers are in contact or vertically separated. Overall, the regional analysis shows a good correlation between the POLDER and the DRM SODA AOTs when the microphysics of aerosols is dominated by fine-mode particles of biomass-burning aerosols from southern Africa (correlation coefficient ( R 2 ) of 0.83) or coarse-mode aerosols of Saharan dust ( R 2 of 0.82). A good correlation between these methods ( R 2 of 0.68) is also observed in the global treatment, when the aerosol and cloud layers are separated well. The analysis of detached layers also shows a mean difference in AOT of 0.07 at 532 nm between POLDER and DRM SODA at a global scale. The correlation between the retrievals decreases when a complex mixture of aerosols is expected ( R 2 of 0.37) – as in the East Asia region – and when the ...