MONTHLY CHARTS OF SURFACE WIND STRESS CURL OVER THE INDIAN OCEAN

MICHAEL HANTEL Meteorological Institute, University of Bonn, West Germany

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Abstract

The surface wind stress curl is the forcing function in the equations of vertically integrated water transport of wind-driven ocean currents. Hence, it has become a basic quantity in theoretical oceanography. As the time dependence of all important surface quantities in the Indian Ocean is stronger than in other oceans, it is valuable to look particularly at the time variation in this region. This study presents monthly charts of the wind stress curl at the surface of the Indian Ocean from its land boundaries up to 50° S. and from 20° E. to 116° E.

Basic data were the monthly surface maps of the Koninklijk Nederlands Meteorologisch Instituut, derived from ship observations and given as 2° square means of the surface wind. The processing of the data is described in detail. In particular, small-scale fluctuations are objectively filtered out.

While earlier compilations are usually on a coarser grid (seasonal and 5° square averages), the present data have a refined time and space resolution. Therefore, they allow one to study more detailed structures. In particular, the charts show that the curl pattern in the Indian Ocean is not independent of longitude.

Abstract

The surface wind stress curl is the forcing function in the equations of vertically integrated water transport of wind-driven ocean currents. Hence, it has become a basic quantity in theoretical oceanography. As the time dependence of all important surface quantities in the Indian Ocean is stronger than in other oceans, it is valuable to look particularly at the time variation in this region. This study presents monthly charts of the wind stress curl at the surface of the Indian Ocean from its land boundaries up to 50° S. and from 20° E. to 116° E.

Basic data were the monthly surface maps of the Koninklijk Nederlands Meteorologisch Instituut, derived from ship observations and given as 2° square means of the surface wind. The processing of the data is described in detail. In particular, small-scale fluctuations are objectively filtered out.

While earlier compilations are usually on a coarser grid (seasonal and 5° square averages), the present data have a refined time and space resolution. Therefore, they allow one to study more detailed structures. In particular, the charts show that the curl pattern in the Indian Ocean is not independent of longitude.

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