The heat exchange between ocean and atmosphere especially in Arctic regions is an important factor influencing the global climate system. Meteorological conditions but also the sea ice concentration (SIC) strongly influence the atmospheric boundary layer structure. In the present study it is shown by application of a mesoscale model to a domain which is typical for one grid cell of a global climate model that the mesoscale distribution of sea ice (subgridscale for the climate model) may have a significant effect on the domain averaged profiles of heat fluxes and of meteorological variables.
For this study the nonhydrostatic atmospheric mesoscale model METRAS is used with a horizontal resolution of 2 km and a total domain of 100 km times 100 km. Winterly off-ice wind conditions are prescribed over the marginal ice zone and a convective boundary layer develops due to the large temperature difference of about 30 degrees between the surface near flow and the open water. The model is run with a nonlocal turbulence closure which allows countergradient heat and moisture fluxes and which has been carefully checked against aircraft observations. The subgridscale sea ice concentration is taken into account by using a flux averaging method which uses the concept of a blending height and takes into account the form drag of ice floes.
Several case studies have been performed where for each model run the same domain averaged SIC has been prescribed but the position of the ice edge and (or) the spatial variations of the SIC are different. The model results show that the most significant differences for the model runs with different sea ice scenarios are found for the domain averaged profiles of the vertical wind velocity and of the humidity. But also the area averaged heat fluxes are influenced significantly (30 percent). In general it can be concluded from our model results
that the mean SIC in the model area and the sea ice distribution are
both influencing the area-averaged heat fluxes. Therefore even in large-scale models some detailed information on the sea ice distribution should be taken into account when calculating heat fluxes.