Modeling Clear‐Sky Cooling Episodes Over Arctic Sea Ice During Polar Night: The Effect of Explicitly Resolved Leads and Realistic Snow Depth

Sea ice surface in the inner Arctic is often oversimplified in coarse‐resolution atmospheric models. Large uncertainties exist in the representation of heat transfer through subgrid‐scale leads. Moreover, some models and reanalyzes neglect snow over ice. In this study, we quantify the effects of explicitly resolved large leads and of realistic snow cover on the near‐surface thermal regime in the central Arctic. To that aim, three clear‐sky cooling episodes are simulated using a mesoscale model. The distribution of leads is prescribed based on MODIS satellite data. Comparison with observations at the drifting station “North Pole‐35” shows that air and surface temperatures are best reproduced when thin ice is prescribed in leads. Prescribing open water in leads results in an overestimation of temperature and in excessive cloud formation. Snow on ice has a cooling effect of a similar magnitude as the warming effect of leads. Both the presence of ice‐covered leads and of snow increases stability over sea ice. At the same time, cloud formation over large open leads results in an increase of downwelling radiation and a decrease of stability. Regionally‐averaged mesoscale model results are in good agreement with results of a simple heat‐balance model. But only in the mesoscale model, leads result in a substantial increase of the regionally‐averaged near‐surface wind speed and momentum flux by up to 15% and 25%, respectively. The obtained results point to possible drawbacks of coarse‐resolution models and reanalyzes and highlight the need for an adequate parameterization of heat and momentum transfer over leads.