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Satellite observations of microwave brightness temperatures between 19 GHzand 85 GHz are the main data sources for operational sea-ice monitoring andretrieval of ice concentrations. However, microwave brightness temperaturesdepend on the emissivity of snow and ice, which is subject to pronouncedseasonal variations and shows significant hemispheric contrasts. Thesemainly arise from differences in the rate and strength of snow metamorphismand melt. We here use the thermodynamic snow model SNTHERM forced byEuropean Re-Analysis (ERA)interim data and the Microwave Emission Model of Layered Snowpacks (MEMLS), to calculate the sea-icesurface emissivity and to identify the contribution of regional patterns inatmospheric conditions to its variability in the Arctic and Antarctic. Thecomputed emissivities reveal a pronounced seasonal cycle with largeregional variability. The emissivity variability increases from winter toearly summer and is more pronounced in the Antarctic. In the pre-melt period(January–May, July–November) the standard deviations in surface microwaveemissivity due to diurnal, regional and inter-annual variability ofatmospheric forcing reach up to Δε = 0.034, 0.043,and 0.097 for 19 GHz, 37 GHz and 85 GHz channels, respectively. Between 2000and 2009, small but significant positive emissivity trends were observed inthe Weddell Sea during November and December as well as in Fram Straitduring February, potentially related to earlier melt onset in these regions.The obtained results contribute to a better understanding of the uncertaintyand variability of sea-ice concentration and snow-depth retrievals inregions of high sea-ice concentrations

The microwave emissivity variability of snow covered first-year sea ice from late winter to early summer: a model study