It  is essential for climate and weather prediction models that the exchange of mass, energy and momentum between atmosphere, ocean and sea ice is modeled close to reality. Researchers  of  section Polar Meteorology  are studying these exchange processes by observations and closely related modeling using the nonhydrostatic mesoscale model METRAS. The main focus of the model applications is on the investigation of the atmospheric boundary layer  structure during different seasons and for different flow regimes and sea ice cover. The model is applied in a wide range of scales with horizontal grid sizes between 100 m and 40 km. Turbulence parameterizations are tested and further developed based on the model results.