Seasonal-Variation in Wind-Speed and Sea State from Global Satellite Measurements

Sandwell, DT, Agreen RW.  1984.  Seasonal-Variation in Wind-Speed and Sea State from Global Satellite Measurements. Journal of Geophysical Research-Oceans. 89:2041-2051.


The GEOS 3 altimeter, which collected data intermittently for nearly 4 years, has measured significant wave heights and surface wind speeds over most of the world's oceans. Using these data, we have constructed contour maps of spatial variations in sea state and wind speed for winter and summer. To obtain reliable averages in the southern oceans, we low-pass filtered the data using a two-dimensional Gaussian filter with a half width of 600 km. The wind speed maps show that the zonal surface wind patterns, such as the westerlies, the horse latitudes, the trade winds, and the doldrums, shift south by about 10° between winter and summer. As expected, the highest wind speeds and sea states occur during the winter months in the mid-latitudes, 30°–60°. The most striking feature of the maps, however, is the large asymmetry in the summer to winter variation between the two hemispheres. The largest seasonal variations in sea state and wind speed occur in the northern hemisphere oceans and especially in the North Atlantic, where there is almost a factor of 2 variation. In contrast, the summer to winter variation in wind speed and sea state in the southern hemisphere oceans is relatively small. For example, the summer to winter increase in wind speed at 50°S is less than 10%, while at 50°N it is more than 50%. This differing variability can be attributed to the asymmetric distribution of continental area between the two hemispheres and the low effective heat capacity of the continents relative to the oceans.