A case study on warm air advection over the Arctic marginal sea ice zoneis presented, which is based on aircraft observations with direct fluxmeasurements carried out in early spring, 1998. A shallow atmosphericboundary layer (ABL) was observed, which was gradually cooling oversea ice. This was mainly due to a strong stable stratification withdownward turbulent heat fluxes of about 10-20 Wm-2 but also due toradiative cooling. Two mesoscale models, a hydrostatic and anon-hydrostatic one with different turbulence closures, were applied.Despite of these fundamental differences between the models, the resultsof the both models agreed well with the observed data. Certain closure assumptions had a more crucial influence on the results than the differencesbetween the models. Such was e.g. the parameterization of the surfaceroughness for momentum (z0) and heat (zT). It strongly affected the windand temperature fields not only close to the surface but also within andabove the temperature inversion layer. The best results were achieved using a z0 that took into account the form drag effect of sea ice ridgestogether with zT = 0.1z0. The stability within the elevated inversionstrongly depended on the minimum eddy diffusivity Kmin. A simple ad hocparameterization seems applicable, where Kmin is calculated as0.005 times the neutral eddy diffusivity. Although the longwave radiativecooling was largest within the ABL, the application of a radiation schemewas less important there than above the ABL. This was related to aninteraction of the turbulent and radiative fluxes. In order to reproduce thestrong inversion, it was necessary to use a vertical and horizontalresolution higher than those applied in most regional and large-scaleatmospheric models.