Linda Thielke, Gunnar Spreen , Marcus Huntemann, Dmitrii Murashkin

Surface temperature is crucial in studying the Arctic climate, particularly during winter. We examine 1 m resolution surface temperature maps of 35 helicopter flights between 02 October 2019 and 23 April 2020, recorded during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC). The seasonal cycle of the average surface temperature spans from 265.6 K on 02 October 2019 to 231.8 K on 28 January 2020. The surface temperature is affected by atmospheric changes and also varies across scales. Furthermore, we concentrate on leads in sea ice because they allow for greater heat exchange between ocean and atmosphere than thick, snow-covered ice. Leads, which appear considerably warmer than sea ice, are classified by a temperature threshold. The local scale (5–10 km) lead area fraction varies between 0% and 4% with a higher variability than on a regional scale (20–40 km), where leads cover a more stable fraction of 0-1% until mid-January when it increases to 4%. The variability in the lead area is caused by sea ice dynamics (opening and closing of leads), as well as thermodynamics with ice growth (lead closing). To understand better the ice rheology throughout the winter, we identify lead orientation distributions. We find that the orientation varies between different flights but the distribution mostly shows one prominent orientation peak. Thus, we are not able to determine predominant intersection angles, which would need two modes in the orientation distribution. The lead width distribution follows a power law with a negative exponent of 2.63, which agrees with literature values, proves the comparability to other datasets, and extends the existing relationship to the smaller scales, as observed here. The appearance of many more small leads compared to wider leads is important since they only occur on the sub-footprint scale of thermal infrared satellite data. Sub-satellite-footprint lead statistics are essential for Arctic-climate investigations because the ocean-atmosphere heat exchange does not scale linearly with lead area fraction and is larger for smaller leads.