Warm air intrusions over Arctic sea ice can rapidly change the snow and ice surfaceconditions and can alter sea ice concentration (SIC) estimates derived from satellite-based microwave radiometry without altering the true SIC.Here we focus on two warm moist air intrusions that produced surface glazing duringthe Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC)expedition that reached the research vessel Polarstern in mid-April 2020. After theevents, we observe increased SIC deviations between different satellite products,including climate data records, and especially an underestimation of SIC for algorithmsbased on polarization difference.To examine the causes of this underestimation, we use the extensive MOSAiC snowand ice measurements to computationally model the brightness temperatures of thesurface on a local scale. We further investigate the brightness temperatures observedby ground-based radiometers at frequencies 6.9 GHz, 19 GHz and 89 GHz.We show that the drop in the retrieved sea ice concentration of some satellite productscan be attributed to large-scale surface glazing, i.e., the formation of a thin ice crust atthe top of the snowpack, caused by the warming events.Another mechanism affecting satellite products which are mainly based on gradientratios of brightness temperatures, is the interplay of the changed temperature gradientin the snow and snow metamorphism.From the two analyzed climate data record products, one is less affected by thewarming events.The low frequency channels at 6.9 GHz were less sensitive to these snow surfacechanges, which could be exploited in future retrievals of sea ice concentration.
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Rückert et al. (2023) studied this question.