Retrieval of aerosol optical depth over the Arctic cryosphere during spring and summer using satellite observations

• Published in: Atmospheric Measurement Techniques
• Main Authors: Swain, Basudev, Vountas, Marco, Deroubaix, Adrien, Lelli, Luca, Ziegler, Yanick, Jafariserajehlou, Soheila, Gunthe, Sachin S., Herber, Andreas, Ritter, Christoph, Bösch, Hartmut, Burrows, John P.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2024
• Subjects: article; Verlagsveröffentlichung; Arctic; Hornsund; Aerosol Robotic Network; arctic cryosphere
• Online Access: https://doi.org/10.5194/amt-17-359-2024; https://noa.gwlb.de/receive/cop_mods_00071123; https://noa.gwlb.de/servlets/MCRFileNodeServlet/cop_derivate_00069427/amt-17-359-2024.pdf; https://amt.copernicus.org/articles/17/359/2024/amt-17-359-2024.pdf

The climate in the Arctic has warmed much more quickly in the last 2 to 3 decades than at the mid-latitudes, i.e., during the Arctic amplification (AA) period. Radiative forcing in the Arctic is influenced both directly and indirectly by aerosols. However, their observation from ground or airborne instruments is challenging, and thus measurements are sparse. In this study, total aerosol optical depth (AOD) is determined from top-of-atmosphere reflectance measurements by the Advanced Along-Track Scanning Radiometer (AATSR) on board ENVISAT over snow and ice in the Arctic using a retrieval called AEROSNOW for the period 2003 to 2011. AEROSNOW incorporates an existing aerosol retrieval algorithm with a cloud-masking algorithm, alongside a novel quality-flagging methodology specifically designed for implementation in the high Arctic region (≥ 72∘ N). We use the dual-viewing capability of the AATSR instrument to accurately determine the contribution of aerosol to the reflection at the top of the atmosphere for observations over the bright surfaces of the cryosphere in the Arctic. The AOD is retrieved assuming that the surface reflectance observed by the satellite can be well parameterized by a bidirectional snow reflectance distribution function (BRDF). The spatial distribution of AOD shows that high values in spring (March, April, May) and lower values in summer (June, July, August) are observed. The AEROSNOW AOD values are consistent with those from collocated Aerosol Robotic Network (AERONET) measurements, with no systematic bias found as a function of time. The AEROSNOW AOD in the high Arctic was validated by comparison with ground-based measurements at the PEARL, OPAL, Hornsund, and Thule stations. The AEROSNOW AOD value is less than 0.15 on average, and the linear regression of AEROSNOW and AERONET total AOD yields a slope of 0.98, a Pearson correlation coefficient of R=0.86, and a root mean square error (RMSE) of =0.01 for the monthly scale in both spring and summer. The AEROSNOW observation of increased AOD ...