AN OBSERVATIONAL STUDY OF THE KATABATIC WIND CONFLUENCE ZONE NEAR SIPLE COAST, WEST ANTARCTICA

A month-long field program to study the springtime katabatic wind conf luence zone (where katabatic winds converge) has been carried out near Siple Coast, West Antarctica. Based on previous observations and nume rical studies, two surface camps, Upstream B (83.5 degrees S, 136.1 de grees W) and South Camp (84.5 degrees S, 134.3 degrees W), were establ ished. Ground-based remote sensing equipment(sodar and RASS), along wi th conventional observations, were used. Combining the analyses of sur face observations and wind and temperature profiles at the above camps , the following picture for the cross-sectional structure of the confl uence zone emerges. A relatively cold katabatic airflow, which probabl y comes from East Antarctica, occupies the layer between the surface a nd roughly 500 m AGL. Low-level jets are present below 200 m AGL and a re stronger near the Transantarctic Mountains. Diurnal variation is pr esent in this cold drainage flow and decreases toward the Transantarct ic Mountains. Weak-inversion-layer tops are found near 500 m AGL, whic h is roughly equal to the depth of the cold katabatic Bow. The warmer West Antarctic katabatic airflow overlies the cold drainage Bow from E ast Antarctica and has a depth of approximately 1000 m at Upstream B a nd more than 1500 m at South Camp; this is caused by blocking of the c onverging West Antarctic airflow by the Transantarctic Mountains. This warm flow originates near the surface far upslope in the vicinity of Byrd Station (80 degrees S, 120 degrees W). A baroclinic zone, formed where the two drainage flows are horizontally adjacent, appears to bec ome unstable with some frequency to generate mesoscale cyclones.