Cloud Microphysics and Radiative Forcing Over West Antarctica from the Atmospheric Infrared Sounder (AIRS)

The new AIRS Version 6 data product provides retrievals of cloud properties including thermodynamic phase, emissivity, effective particle size, and effective cloud amount. These retrievals are becoming available just as interest has grown over climate warming throughout West Antarctica. In this study, we examine summertime AIRS retrievals over Antarctica, and we compare West versus East Antarctica, and both regions under the influence of positive versus negative polarity in the Southern Annular Mode (SAM) index. Over West Antarctica, a positive SAM index polarity is associated with increases in cloud amount and emissivity, which together increase the surface longwave radiation by 4.2 – 6.3 Watts per square meter, relative to a negative SAM index polarity. In contrast, over East Antarctica, a positive SAM index polarity is associated with decreases in cloud amount and emissivity, which together decrease the surface longwave radiation by up to -10.2 Watts per square meter. Over both regions, a positive SAM index polarity is associated with smaller fractions of both ice and liquid water, and an increase in indeterminate phase as specified by AIRS data, which may be either mixed-phase cloud, or supercooled liquid water. AIRS-retrieved cloud emissivity generally shows positive correlation with Automatic Weather Station (AWS) measurements of surface temperature over the Antarctic continent, but with widely varying strength and statistical significance.