Comparison Of Global Ocean Mean Monthly Waves Swell And Surface Winds For The Boreal Summers Of 1978 And 1987 From Seasat And Geos

Abstract

Radar altimeter observations of the global ocean, first acquired by SEASAT during the boreal summer of 1978, were repeated by GEOSAT during the boreal summer of 1987. The same algorithm, applied to both sets of observations, has produced mean monthly significant wave heights, minimum swell heights, and surface wind speeds of the global ocean for these two summers. Although the mean monthly wind speed fields for both 1978 and 1987 show the zonal banding found in various ocean climate atlases, they also show many mesoscale features, on scales of the order of 1000 km, which do not appear in the atlases. They also show that these large scale and mesoscale features exhibit strong variations between the two summers. These features include the increased wind speeds in the northern I ndian ocean that are associated with the summer monsoons which reach a maximum areal extent and speed in August and disappear in September. This feature was evident in both 1978 and 1987; however, in 1978 the mean monthly winds were stronger and significant wave heights were greater by 25 percent than in 1987. The observations show that the highest wind speed and waves occurred in the Southern Ocean with the following difference. In 1978 there was a pronounced eastward migration around Antarctica of the regions of maximum wind speeds and waves from July through September. In 1987, this eastward migration did not occur; the wind speeds and wave height maximums occurred in August throughout the Southern ocean. The distributions and variations of winds, waves, and swell for both summers in the regions of the Westerlies, Trade Winds, Doldrums are discussed and compared.