The impact of form drag on atmospheric transfer coefficients over fractional sea ice cover for neutral and non-neutral stability

A realistic modeling of atmospheric processes over polar sea ice needs a detailed representation of the near-surface atmospheric fluxes of momentum and heat. Transfer coefficients should account for the inhomogeneous distribution of roughness elements and surface temperature caused by fractional sea ice cover. Previous studies show that form drag caused by edges of ice floes and melt ponds needs to be taken into account in the parametrization of the drag coefficient.

In the present contribution a recently developed parametrization including form drag will be compared with parametrizations currently used in climate models. An application of the parametrizations to different sea ice scenarios and with an atmospheric forcing as being typical for Arctic summer shows that the traditionally used drag coefficients without form drag differ from the new ones by a factor 0.5-1.2 dependent on the region.

Furthermore, we show that the existence of form drag affects both momentum and heat transfer coefficients. We investigate the stability dependence of both coefficients and discuss different strategies to account for this dependence. Finally, stability corrections are proposed which are based on the traditional Louis (1969) concept. Thus they can be easily implemented in climate models. A first application of the new concept in a global climate model (ECHAM6-FESOM) reveals the potentially large impact of the new parametrizations on simulations of the coupled Arctic climate system.