Air-Sea Exchange of Momentum and Sensible Heat Over the Baltic Sea

Sammanfattning: Long term measurements are used to explore the wave impact on the momentum and sensible heat transfer in the marine atmospheric surface layer. This is important in determining the boundary conditions of atmosphere-ocean coupled models of many scales. In those models classical similarity theories developed over land are commonly used, but they have shown to be questionable over sea. It is found that during pure wind sea conditions, the wind law, which is valid over land, is also valid over the sea. The sea surface roughness resembles that of a solid rigid surface. It scales with the surface elevation and decreases with wave age. When the sea surface is dominated by swell, wave influence is felt through the whole boundary layer. The wind profile is shown to be a function of wave state, and the classical wind law is modified when swell is present. Measurements and a wind over wave coupled model reveal that the momentum exchange depends on a combination of wind and wave condition. The exchange of sensible heat does not show the similar dependence on the wave state as the momentum. However at strong winds when waves break, the effect of spray becomes significant, increasing the exchange coefficient considerably.