The ocean surface wind field near South Georgia Island, Antarctica

Sixteen months of QuikSCAT scatterometer surface wind stress measurements are used to investigate wind forcing of the upper ocean in the vicinity of South Georgia Island in the southwestern Atlantic Ocean. Although only 170 km in length and less than 35 km wide, South Georgia is mountainous, with 13 distinct peaks exceeding 2000 m altitude. The steep topography significantly perturbs the tropospheric wind field, leading to upwind blocking and stress divergence, large areas of accelerated winds near the island extremities, and long downwind wake-like regions.

The QuikSCAT/SeaWinds data provides spatially extensive, all-weather vector wind measurements with high (12.5 - 25 km) spatial resolution. The high latitude and QuikSCAT orbit allow virtually complete coverage of the South Georgia Island study area approximately every 12 hours.

Although significant topographic wind perturbations are not evident in operational ECMWF or NCEP surface analyses, conditional QuikSCAT mean wind climatologies (based on far-field wind direction) show that corner acceleration and downwind shadow features are robust features of the climatological surface wind field within 400 km of the island. The orographically induced changes in wind stress magnitude and direction lead to characteristic curl and divergence patterns which can drive significant ocean circulations with vertical velocities exceeding 1 m/day over areas of several hundred square kilometers.

In addition to constructing conditional climatologies, the QuikSCAT data are investigated on a pass-by-pass basis to determine the quantitative dependences of acceleration and wake area, orientation, and maximum extent on large-scale synoptic conditions such as overall surface wind speed/direction and Froude number.

Special Session on Air-Sea Interaction Studies Using Satellite Observations