5b.8
Topographic forcing of the Antarctic wind field
Thomas R. Parish, University of Wyoming, Laramie, WY
The near-surface wind regime over the Antarctic continent is among the most persistent on earth. Time-averaged winds are intimately tied to the orientation and slope of the underlying ice terrain, which has suggested that local terrain influences are critical to the establishment of the wind fields. Katabatic winds are an obvious example of terrain-generated flows. These gravity-driven flows arise due to radiative cooling of the sloping surface. Observations, however, also show that Antarctic near-surface flows display high values of directional constancy throughout the summer period during which time katabatic winds should not prevail. In addition, the coastal margin about Antarctica is among the most active regions for extratropical cyclones on the globe. Frequent and intense cyclonic disturbances encircle the continent throughout the year. Despite the profound changes in the horizontal pressure field accompanying these cyclones, near-surface wind directions show surprisingly little variation. The Antarctic wind field is thus remarkably robust.
A series of numerical experiments were performed with the Penn State/NCAR Mesoscale Model (MM5) to examine the role of the Antarctic continent in shaping the low-level wind field. Results show that the forcing of stable air against the steep coastal escarpment is accompanied by significant adjustment of mass and wind fields similar to that observed during a "barrier wind" event. It is this adjustment process that is responsible for the remarkable persistence of the Antarctic surface winds associated with intense cyclone activity. From a forecasting perspective, surface winds over the continental ice slopes show little relationship to the large-scale horizontal pressure field to the north of the continent and hence traditional analyses relating the wind to the synoptic environment are misleading.
Session 5b, Polar Weather Forecasting (Parallel with Session 5A)
Friday, 18 May 2001, 8:00 AM-10:00 AM
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