Evaluation of Unambiguous Vector Winds from the Seasat Scatterometer

Abstract

Ambiguity in wind direction has long been an impediment to applications of wind observations from the Seasat scatterometer (SASS). Three months of unambiguous global SASS vector winds (7 July-IO October 1978) have recently become available from the Goddard Space flight Center (GSFC) Laboratory for A~oSPheric Sciences. The directional ambiguities were removed objectively through the use of an atmosphenc general circulation model. Elimination of the directional ambiguities greatly enhances the utility of the SASS wind observations. Atmospheric and oceanographic applications 9f the GSFC vector wind data are given in two companion papers. The GSFC SASS vector wind dataset has potential utility for many applications, so it is useful to assess the data quality. In this paper, the GSFC data are compared with 14 days of SASS vector winds from the !et Propulsion Laboratory for which the directional ambiguities were subjectively removed by trained meteorologISts using pattern recognition techniques. Both methods are shown to be statistically very similar over the l4-day period. The two methods chose the same solution about 73% of the time and nearest-neighbor solutions about 20% of the time. Reasons for discrepancies are examined and it is concluded that the methods tend to disagree most often in regions oflow wind speed and/or highly variable wind direction. The directional differences are generally small and random so that there are no significant differences between spatially and temporally averaged wind fields constructed from the two datasets.