Abstract
Abstract. Observations of sea-ice concentration are available from satellites year-round and almost weather-independently using passive microwave radiometers at resolutions down to 5 km. Thermal infrared radiometers provide data with a resolution of 1 km but only under cloud-free conditions. We use the best of the two satellite measurements and merge thermal infrared and passive microwave sea-ice concentrations. This yields a merged sea-ice concentration product combining the gap-free spatial coverage of the passive microwave sea-ice concentration and the 1 km resolution of the thermal infrared sea-ice concentration. The benefit of the merged product is demonstrated by observations of a polynya which opened north of Greenland in February 2018. We find that the merged sea-ice concentration product resolves leads at sea-ice concentrations between 60 % and 90 %. They are not resolved by the coarser passive microwave sea-ice concentration product. The benefit of the merged product is most pronounced during the formation of the polynya. Next, the environmental conditions during the polynya event are analysed. The polynya was caused by unusual southerly winds during which the sea ice drifted northward instead of southward as usual. The daily displacement was 50 % stronger than normal. The polynya was associated with a warm-air intrusion caused by a high-pressure system over the Eurasian Arctic. Surface air temperatures were slightly below 0 ∘C and thus more than 20 ∘C higher than normal. Two estimates of thermodynamic sea-ice growth yield sea-ice thicknesses of 60 and 65 cm at the end of March in the area opened by the polynya. This differed from airborne sea-ice thickness measurements, indicating that sea-ice growth processes in the polynya are complicated by rafting and ridging. A sea-ice volume of 33 km3 was produced thermodynamically.
Highlights
Arctic sea ice influences the climate system by radiating incident heat back into space and by regulating the ocean– atmosphere exchange of heat, humidity and momentum
Moderate Resolution Imaging Spectroradiometer (MODIS) and Advanced Microwave Scanning Radiometer 2 (AMSR2) sea-ice concentration (SIC), we find that AMSR2 SIC is higher than MODIS for high SIC
We find that the Synthetic Aperture Radar (SAR) and MODIS SIC are higher than the AMSR2 SIC
Summary
Arctic sea ice influences the climate system by radiating incident heat back into space and by regulating the ocean– atmosphere exchange of heat, humidity and momentum. The fraction of a given ocean area which is covered by sea ice is called sea-ice concentration (SIC). SIC is of high relevance for physics, biology and the safety of shipping routes. The summer sea-ice retreat observed since 2007 is a major driver of the Arctic amplification, the enhanced warming of the Arctic compared to the mid-latitudes (Dai et al, 2019). While the scientific community largely agrees that Arctic amplification changes the mid-latitude weather patterns, the exact mechanisms and pathways are subject to debate. A comprehensive literature synthesis is given in Vavrus (2018)
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