<title>Variability of the wind field in the tropical oceans as observed by satellite sensors</title>

Abstract

The wind stress is the primary force driving the tropical oceans from daily to interannual time scales. Conventional measurements from ships of the wind vectors are not available with a sufficient quality regarding data accuracy as well as their coverage. Satellite observations of the surface wind over the sea are now available on a routine basis at the Institut Francais de Recherche pour l'Exploitation de la Mer (IFREMER), derived from the European Remote Sensing-1 (ERS-1) scatterometer and altimeter and from the radiometer special sensor microwave/imager (SSM/I). More than 3 years of weekly stress fields (1991-1994) with a resolution of one degree in latitude and longitude are produced using an objective analysis method. The accuracy of these gridded winds was evaluated by comparison with TAO buoys in the tropical Pacific area (Riou, 1995). The root mean square differences are of the order of 1.2 m/s and 15 degrees. The greatest differences are observed in the TOGA/COARE region where the wind variability is largest on the weekly scale. The low frequencies (monthly to interannual) of the wind variability are discussed and compared to those obtained from the TAO buoys. In this paper the time and space scales of the sea surface wind are described using a complex EOF analysis. One of the most interesting results is that the weekly averaged wind fields derived from ERS-1 scatterometer are useful to depict a 30-50 day oscillation over the tropical Pacific Ocean.