An Observational Study of the Katabatic Wind Confluence Zone near Siple Coast, West Antarctica

David H. Bromwich Polar Meteorology Group, Byrd Polar Research Center and Atmospheric Sciences Program, The Ohio State University, Columbus, Ohio

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Zhong Liu Polar Meteorology Group, Byrd Polar Research Center and Atmospheric Sciences Program, The Ohio State University, Columbus, Ohio

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Abstract

A month-long field program to study the springtime katabatic wind confluence zone (where katabatic winds converge) has been carried out near Siple Coast, West Antarctica. Based on previous observations and numerical studies, two surface camps, Upstream B (83.5°8, 136.1°W) and South Camp (84.5°S, 134.3°W), were established. Ground-based remote sensing equipment (sodar and RASS), along with conventional observations, were used. Combining the analyses of surface observations and wind and temperature profiles at the above camps, the following picture for the cross-sectional structure of the confluence zone emerges. A relatively cold katabatic airflow, which probably comes from Fast Antarctica, occupies the layer between the surface and roughly 500 m ACL. Low-level jets are present below 200 m AGL and are stronger near the Transantarctic Mountains. Diurnal variation is present in this cold drainage flow and decreases toward the Transantarctic Mountains. Weak-inversion-layer tops are found near 500 m AGL, which is roughly equal to the depth of the cold katabatic flow. The warmer West Antarctic katabatic airflow overlies the cold drainage flow from East Antarctica and has a depth of approximately 1000 m at Upstream B and more than 1500 m at South Camp; this is caused by blocking of the converging West Antarctic airflow by the Transantarctic Mountains. This warm flow originates near the surface far upslope in the vicinity of Byrd Station (80°S, 120°W). A baroclinic zone, formed where the two drainage flows are horizontally adjacent, appears to become unstable with sonar frequency to generate mesoscale cyclones.

Abstract

A month-long field program to study the springtime katabatic wind confluence zone (where katabatic winds converge) has been carried out near Siple Coast, West Antarctica. Based on previous observations and numerical studies, two surface camps, Upstream B (83.5°8, 136.1°W) and South Camp (84.5°S, 134.3°W), were established. Ground-based remote sensing equipment (sodar and RASS), along with conventional observations, were used. Combining the analyses of surface observations and wind and temperature profiles at the above camps, the following picture for the cross-sectional structure of the confluence zone emerges. A relatively cold katabatic airflow, which probably comes from Fast Antarctica, occupies the layer between the surface and roughly 500 m ACL. Low-level jets are present below 200 m AGL and are stronger near the Transantarctic Mountains. Diurnal variation is present in this cold drainage flow and decreases toward the Transantarctic Mountains. Weak-inversion-layer tops are found near 500 m AGL, which is roughly equal to the depth of the cold katabatic flow. The warmer West Antarctic katabatic airflow overlies the cold drainage flow from East Antarctica and has a depth of approximately 1000 m at Upstream B and more than 1500 m at South Camp; this is caused by blocking of the converging West Antarctic airflow by the Transantarctic Mountains. This warm flow originates near the surface far upslope in the vicinity of Byrd Station (80°S, 120°W). A baroclinic zone, formed where the two drainage flows are horizontally adjacent, appears to become unstable with sonar frequency to generate mesoscale cyclones.

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