C054-0004
Extreme ice sheet melting over Antarctica during the 2019-2020 austral melt season observed by the SMAP L-band Microwave Radiometer

Tuesday, 15 December 2020
Poster
Mohammad Mousavi, NASA Jet Propulsion Laboratory, Pasadena, CA, United States, Andreas Colliander, Jet Propulsion Laboratory, Pasadena, CA, United States, Julie Miller, University of Colorado at Boulder, Cooperative Institute for Research in Environmental Sciences, Boulder, CO, United States and John S Kimball, The University of Montana, Numerical Terradynamic Simulation Group, W.A. Franke College of Forestry & Conservation, Missoula, MT, United States
Abstract:
Monitoring the melt extent and duration of Antarctica ice shelves and coastal areas is important for Antarctica climate and ice sheet stability analysis. For example, intense surface melting over several years can lead to ice shelf collapse and disintegration. Due to their all-weather operational capability and sensitivity to the presence of liquid water in snow and firn, both microwave radar and radiometer systems have been long used as tools to detect melt events over ice sheets from space.

We investigated the response of the L-band (1.4 GHz) radiometer on NASA’s Soil Moisture Active Passive (SMAP) satellite mission, launched in January 2015, to ice sheet melt events. These measurements have ~38 km resolution, and the data are gridded on a 9-km polar equal-area projection grid for this study. The satellite has a sun-synchronous 6AM/6PM equator-crossing orbit, a constant 40° sensor incidence angle, and an approximately 1000-km swath width. This enables the coverage of Antarctica once daily in AM overpasses and once daily in PM overpasses per day. The radiometric resolution of the gridded SMAP TB is ~0.5 K.

The presence of even a small amount of liquid water in the snowpack can significantly impact microwave measurements. While L-band measurements are less sensitive to liquid water than the traditionally used Ku- and Ka-band measurements, we have found that the L-band polarization difference exhibits clear sensitivity to melt events. On the account of the lesser sensitivity to melt effects, however, L-band measurements do not saturate as quickly as the Ku- and Ka-bands, which enables detection of a range of melting conditions corresponding to melt severity. Our melt detection algorithm uses a normalized polarization ratio (NPR) and examines the NPR departure from winter conditions during the melt season.

Results show intense surface melting on the West Antarctic Ice Sheet during the 2019-2020 austral melt season, even though the overall extent was typical compared to the previous austral melt seasons mapped by SMAP. This intense surface melting was observed over all the large ice shelves in the Antarctica Peninsula, such as Larsen C, Larsen D, Wilkins, George VI, Bach, and Stange. In addition, several ice shelves along the northern Amundsen-Bellingshausen Sea coast that typically experience low intensity melting events, such as Abbot, Venable, Cosgrove, and Pine Island experienced intense surface melting.

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