Airborne Observations and Modelling of the Atmospheric Boundary Layer over the Ronne Polynya, Antarctica

In February/March 2010 the Alfred Wegener Institute for Polar and Marine Research (AWI) and the British Antarctic Survey (BAS) carried out the Joint Airborne Study of the Peninsula Region (JASPER) in the Antarctic. Airborne observations of the atmospheric boundary layer over the Ronne Polynya Region were conducted using two research aircraft. The study had two main goals: first, to compare and verify the aircraft boundary layer measurements between the two aircraft and second, to study the local polynya effect in the Weddell Sea ice area. The wind, temperature and turbulent flux observations of both aircraft showed a good agreement. We investigated energy and momentum fluxes and the vertical boundary layer structure along cross-sections and profiles over the polynya in different stages of its development. The observations showed that differences in the polynya width and thickness of the nilas cover strongly influenced the turbulent fluxes and structure of the atmospheric boundary layer. We observed a large variability of fluxes along the horizontal flight tracks. Observations orthogonal to the polynya showed the internal boundary layer development starting at the Ronne Ice Shelf and developing over the polynya. We observed a strong decrease in surface and air temperature with distance from the Ronne Ice Shelf front, a decrease in heat fluxes, and an increase in the sea surface albedo. These results reflect the influence of sea ice cover on the boundary layer structure. We studied the spatial development of the atmospheric boundary layer by modelling the flow over the Ronne Polynya with the non hydrostatic meso-scale model METRAS. The model results were validated against the observations of the two research aircraft. The validation of the model against the observations revealed that both mean and turbulent quantities can be well modelled when the transfer coefficients of heat and momentum agree well with observations. Based on the model results the impact of the Ronne polynya on the atmospheric boundary layer far downstream is discussed.