The structure of the polar ABL is influenced by large scale advection of heat and moisture and by local processes. These are turbulent and radiation processes which both depend on the sea ice surface characteristics, but also on low level clouds.
Cold-air outbreaks represent an example for the strong impact of turbulence. During such events cold air masses which are advected from the inner polar regions are strongly heated over the open ocean. The generated turbulence can lead to an increase of the ABL thickness from e.g. 100 m over sea ice to 2 km in a downstream distance of 200 km to the marginal sea ice zone. On the contrary, during on-ice flow regimes radiative cooling of air over sea ice can lead to very shallow ABLs caused by radiative cooling. The resulting stable stratification suppresses strongly the turbulent motions.
Turbulent processes depend on the difference between air and surface temperature and thus also on sea ice characteristics as concentration (lead cover) and ice thickness. But also the surface topography (sea ice pressure ridges, edges of floes and ponds) plays an important role for the generation of turbulent eddies. Snow and melt pond cover and especially cloud cover have a large impact on radiation processes. All the relevant parameters show a strong spatial variability, which forms a large challenge for the derivation of turbulence parametrizations. This holds especially for climate models with grid sizes being much larger than the spatial scale of sea ice inhomogeneity.
AWI researchers of the Section Polar Meteorology have investigated these regimes in the past years by many case studies (modeling and measurements). Based on the results, turbulence parameterizations have been developed for strong convective flow, for near-surface fluxes over sea ice in the inner polar ocean regions and over the marginal sea ice zone with specific conditions. Also the strong impact of convection over leads (channels in sea ice) has been investigated.