Impuls- und Wärmeaustausch zwischen der Atmosphäre und dem eisbedeckten Ozean

Polarstern (PS) cruise ARK XII led into the Laptev Sea and into the Kara Sea. Measurements of atmospheric processes within the polar surface layer were performed by a turbulence probe mounted at the bow crane of the ship.The meteorological conditions during the cruise were characterised by moderate winds and low temperature differences between the atmosphere and the underlying surface.Detailed information about the variation of meteorological parameters and of the surface fluxes were achieved as a function of the surface characteristics. The measurements are used to analyse small scale processes such as the atmospheric flow over polynjas and over pressure ice ridges. The studies allow a general insight into the physics of boundary layer flow over the ice covered ocean and they provide helpful data to initialize and to verify model calculations of small scale processes in the polar boundary layer.The form drag concept is used to calculate the total vertical turbulent flux over the ice covered oceanas the sum of a skin drag effect and of a form drag effect. In polar regions, the latter results from the aerodynamic resistance of obstacles such as ice ridges and floes edges while the skin drag is given by the surface drag of a rather smooth ice field. Improved formulations for the coefficient of resistance of single ice ridges and for the shadowing effect leeward of a ridge are derived by the PS measurements and are implemented to the form drag concept. Shipborne and airborne measurements are used to validate the concept and a good agreement between measured and calculated values of the transfer coefficient of momentum is achieved. Sensitivity studies show, that the shadowing of the wind field due to densely distributed ice ridges does not significantly reduce the form drag of an ice field under realistic sea ice conditions and that the effect of densitystratification on the exchange of momentum is neglectable for typical atmospheric conditions during summertime.