Simulation of the Mesocyclonic Activity in the Ross Sea, Antarctica

The mesocyclonic activity in the southwestern Ross Sea is examined, with emphasis on its forcing by katabatic winds. The three-dimensional version of the meso-gamma-scale primitive equation model Modele Atmospherique Regional is used in which a representation of cloud microphysical processes has been introduced. Idealized boundary conditions are prescribed. In particular, the ocean is assumed to be completely ice-free or partially ice-covered. The former case corresponds to a fall situation that coincides with the climatological maximum of estimated precipitation at McMurdo Station on Ross Island. Due to the propagation of katabatic winds over the ocean, boundary layer fronts form. Clouds are generated in the fronts. A surface pressure trough also forms and extends northeastward from Terra Nova Bay. Mesocyclones are simulated in the trough. When the ocean is ice-free, strong sensible heat fluxes toward the atmosphere amplify the strength of the trough up to typically observed values. Tn this case, snow precipitation is associated with the boundary layer fronts and occurs in particular over McMurdo Sound. It is also found that latent heat release due to precipitation formation in the fronts does not significantly affect the deepening of the trough