Boundary layer over leads ( DFG - funded project, 2007 - 2010)
The physics of turbulence over Antarctic leads and polynyas and its parameterization: a joint study using observations, LES, and a micro-/mesoscale model
Principal investigators: Christof Lüpkes (AWI), Siegfried Raasch (Universität Hannover, IMUK)
In regions with large sea ice concentrations there are always open water areas called leads or polynyas depending on their shape. The length of leads varies between a few kilometres and tens of kilometres and their width ranges from several meters to kilometres. The strong sensible and latent heat fluxes above such areas can trigger convection which significantly modifies the atmospheric boundary layer (ABL). For this reason leads are supposed to have a large influence on the energy exchange between the polar ocean and the atmosphere.
Polynya in the Barents Sea observed in March 2003 during the Winter Arctic Polynya Study (WARPS) of AWI
Satellite image (terra modis, 250 m resolution) with leads in the Antarctic sea ice, observed on 29 10 2005, at about 62 S 0 E north of Neumayer.
The goals of this project are to get a better understanding of the still not well understood effects of leads and polynyas on the boundary layer turbulence and to clarify their importance for the energy budget and structure of the ABL.
Results of the LES model PALM and new helicopter based observations of turbulence over leads will be used to (further) develop parameterizations of the lead effect which can be used in models with different grid sizes ranging from microscale non eddy resolving models to weather forecast and regional climate models. The parameterizations are tested in the nonhydrostatic model METRAS.
Modelled temperature (K) (top) and heat fluxes (W/m2) over a lead of 1 km width as function of height and distance form the upstream lead boundary (wind from left to right). The model METRAS is used here with a new turbulence parameterization for microscale modelling of convection in non-eddy resolving mode.