DYNAMICS OF THE KATABATIC WIND CONFLUENCE ZONE NEAR SIPLE COAST, WESTANTARCTICA

The surface wind pattern over the ice sheets of Antarctica is irregula r with marked areas of airflow confluence near the coastal margins. Wh ere cold air from a large interior area of the ice sheet converges (a confluence zone), an anomalously large supply of air is available to f eed the coastal katabatic winds, which, as a result, are intensified a nd more persistent. The confluence zone inland of Siple Coast, West An tarctica, differs from its East Antarctic counterparts in that the ter rain slopes become gentler rather than steeper as the coast is approac hed. In addition, synoptic processes exert substantially more impact o n the behavior of the surface winds. A month-long field program to stu dy the dynamics of the springtime katabatic wind confluence zone has b een carried out near Siple Coast. Two sites, Upstream B (83.5 degrees S, 136.1 degrees W) and South Camp (84.5 degrees S, 134.3 degrees W), were established roughly perpendicular to the downslope direction. The held program involved the use of the ground-based remote sensing equi pment (sodar and RASS) along with conventional surface and balloon obs ervations. Previous analyses revealed the cross sectional structure of the confluence zone as consisting of a more buoyant West Antarctic ka tabatic airflow overlying a less buoyant katabatic airflow originating from East Antarctica. The force balances inside the confluence zone a re here investigated for three situations: mean (all available wind pr ofiles from balloon launches), and two extreme cases (light and strong winds). A linear regression method is used to estimate the mean verti cal wind shears and horizontal temperature gradients. The vertical win d shears are used to examine whether or not the airflows are in geostr ophic balance. The results are 1) the airflow above the surface at bot h sites is in geostrophic balance for the three situations; 2) inside the West Antarctic katabatic wind zone, there are three forces in the north-south direction-the restoring pressure gradient force associated with blocking of the katabatic and synoptic winds, the downslope buoy ancy force, and the synoptic pressure gradient force associated with t he time-averaged low in the South Pacific Ocean; 3) above the West Ant arctic katabatic wind layer, the observed easterly wind is due to the synoptic pressure gradient force associated with the low; 4) inside th e East Antarctic katabatic wind zone, in addition to the above three f orces, there is the downslope buoyancy force associated with the inver sion; and 5) large-scale transient synoptic systems strongly influence the downslope wind speed and the boundary layer depth, resulting in t he light and strong wind cases.