Global Wind Stress and Sverdrup Circulation from the Seasat Scatterometer

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  • 1 College of Oceanography, Oregon State University, Corvallis, Oregon
  • | 2 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California
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Abstract

Three months of vector wind observations from the Seasat-A satellite scatterometer (SASS) are used to construct gridded fields of monthly average wind stress and wind stress curl over the global ocean. These fields are examined to identify features either poorly resolved or not present in wind stress fields constructed from conventional data. Particular attention is focused on the spatial structures in the high southern latitudes and the tropical regions. The SASS wind stress fields are compared globally with the Hellerman and Rosenstein climatological monthly average surface wind stress fields and with monthly averages of wind stress computed from contemporaneous 1000 mb wind analyses produced by the National Meterological Center.

The potential for satellite scatterometry improving the present knowledge of the global wind stress field and making important contributions to ocean modeling is demonstrated by comparison of global maps of the Sverdrup circulation computed from 3-month average SASS and Hellerman and Rosenstein climatological wind stress curl fields. Except for the region south of about 35°S, the two estimates of Sverdrup circulation are generally very similar. The transports of the western boundary currents calculated from the climatological wind stress fields are consistently higher because the drag coefficient used by Hellerman and Rosenstein is too large by approximately 19%. In the Antarctic Circumpolar Current region, the difference between the two estimates of zonal transport is very large, even disagreeing in direction in the region south of Australia and New Zealand. Historical hydrographic data suggest a tendency, albeit less extensive, for the westward Sverdrup transport indicated by the SASS data, suggesting the possibility of deficiencies in the climatological wind stress fields.

Abstract

Three months of vector wind observations from the Seasat-A satellite scatterometer (SASS) are used to construct gridded fields of monthly average wind stress and wind stress curl over the global ocean. These fields are examined to identify features either poorly resolved or not present in wind stress fields constructed from conventional data. Particular attention is focused on the spatial structures in the high southern latitudes and the tropical regions. The SASS wind stress fields are compared globally with the Hellerman and Rosenstein climatological monthly average surface wind stress fields and with monthly averages of wind stress computed from contemporaneous 1000 mb wind analyses produced by the National Meterological Center.

The potential for satellite scatterometry improving the present knowledge of the global wind stress field and making important contributions to ocean modeling is demonstrated by comparison of global maps of the Sverdrup circulation computed from 3-month average SASS and Hellerman and Rosenstein climatological wind stress curl fields. Except for the region south of about 35°S, the two estimates of Sverdrup circulation are generally very similar. The transports of the western boundary currents calculated from the climatological wind stress fields are consistently higher because the drag coefficient used by Hellerman and Rosenstein is too large by approximately 19%. In the Antarctic Circumpolar Current region, the difference between the two estimates of zonal transport is very large, even disagreeing in direction in the region south of Australia and New Zealand. Historical hydrographic data suggest a tendency, albeit less extensive, for the westward Sverdrup transport indicated by the SASS data, suggesting the possibility of deficiencies in the climatological wind stress fields.

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