DYNAMICAL CONSTRAINTS ON KATABATIC WIND CESSATION IN ADELIE LAND, ANTARCTICA

The katabatic wind events observed in the coastal zone of Adelie Land, Antarctica, on 27 November and 3 December 1985 are simulated with a h ydrostatic mesoscale atmospheric model coupled to a snow moder. The di urnal cycle of insolation is strong. The main difference in the forcin g between the two events is the large-scale wind, which is weak on 27 November and moderate on 3 December. In both cases temperature and win d are characterized by well-marked diurnal cycles. In particular, kata batic winds blow during nighttime and upslope winds during daytime. In both cases the katabatic airstream slows down progressively over the ocean. Consequently, continental air piles up and this generates a poo l of cold air responsible for a pressure gradient force opposing the k atabatic wind. An amplification of the slowing down results. When, in the morning, insolation increases, the surface inversion weakens but t he influence of the cold air pool increases. The katabatic how starts to decay over the coastal zone and then retreats progressively toward the ice sheet interior. When the large-scale wind is weak, the surface warming is sufficient for generating an additional upslope bouyancy f orce, and anabatic flow develops over the ice sheet in the afternoon. When the large-scare wind is moderate and downslope, the pilling up of cold air is important and this has a dramatic impact on the flow. A s harp spatial transition is generated between downslope and upslope win ds over the ocean. This discontinuity moves toward the ice sheet inter ior in the morning and is responsible for the sudden cessation of the katabatic flow seen by static observers. The results of the simulation s are used in order to refine a simple parameterization of Antarctic k atabatic winds.