On the seasonal inconsistency of altimeter wind speed algorithms

Altimeter-derived wind speed has become a major source of data for climatological studies in recent years, thanks to the continued success of several operational missions. A variety of algorithms have been proposed to convert altimeter-measured radar cross-section to sea surface wind speed. The performance of these algorithms determines, to a large extent, the quality of the estimated wind speeds and, consequently, their suitability for various applications. In this study, 6 years of coincident TOPEX altimeter and JMA (Japan Meteorological Agency) buoy wind speeds from January 1993 to December 1998 were used to evaluate the seasonal consistency of three algorithms. Our results demonstrate that seasonal inconsistency is a common problem associated with altimeter wind speed algorithms. A biased pattern of seasonal wind speed variation is inevitable as long as available altimeter algorithms are used in their present forms. The type and extent of the distortion depend on specific algorithm and actual wind speed distribution. It is shown that such a systematic error may have a number of potential consequences, which could undermine some of the geophysical interpretations concerning the seasonality of global and regional wind climate.