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Flow regimes influencing turbulent air - sea ice/ocean interaction

Three main flow regimes can be defined with different atmospheric boundary layer (ABL) structure and turbulence.

The first is the regime of coldair outbreaks which occur in Arctic regions very often between October and April. This regime is characterized by the existence of strong organized roll convection over the open ocean and by large fluxes of sensible heat. Over large regions surface fluxes are in the order of hundreds of W/m2 which leads to strong cooling and heating  of ocean and atmosphere, respectively.

 

The second regime is the on-ice airflow developing during warm air advection across the marginal sea ice zone. Turbulent fluxes of sensible heat are small (~20 W/m2 ) and directed downward so that the atmosphere is warming the sea ice surface.

 

The third regime is the flow over the central polar ocean with large sea ice cover. Similar as in the second regime the ABL is shallow and mostly stably stratified or close to neutral with a strong capping inversion. The stable stratification  is  mainly caused by radiative cooling, but also by other processes such as convective heat transport from leads. Turbulent transports of energy and momentum in the ABL depend strongly on the sea ice cover characterized e.g., by its concentration (lead cover), thickness, surface topography, snow thickness and other parameters. The sea ice properties vary on small spatial scales, which forms a challenge for the derivation of turbulence parameterizations, especially with respect to climate models with grid sizes much larger than the scale of sea ice inhomogeneity.

AWI researchers of Polar Meteorology have investigated these regimes in the past years by many case studies (modeling and observation). Based on the results, turbulence parameterizations have been developed for strong convective flow, for surface fluxes over rough sea ice  and over the marginal sea ice zone, and for the convection over leads.

Satellite image showing the typical cloud structure during a coldair outbreak in the Svalbard region


 
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