Evidence of Time-dependent Sverdrup Circulation in the South Pacific from the Seasat Scatterometer and Altimeter

Abstract

Seasat scatterometer and altimeter data are analyzed to investigate time-dependent Sverdrup dynamics in the Southern Ocean (40°S to 60°S) over seasonal time scales. Sverdrup dynamics are shown to be inadequate to describe the circulation in the South Atlantic and Indian oceans. The Sverdrup circulation in the South Pacific is reasonable north of 55°S. The changes in Sverdrup circulation from July to September 1978 indicate an eastward acceleration along 55°S and westward acceleration along 40°S, suggesting a southward shift in the subpolar eastward flow. Sea level in the South Pacific is estimated for July and September 1978 from scatterometer vector wind data based on Sverdrup dynamics assuming a flat-bottom ocean with barotropic flow. The changes in Sverdrup sea level are compared with the changes in sea level observed by the altimeter for the same time period. Both estimates indicate a rise in sea level along a zonal band centered at about 50°S. This sea level rise inferred from both the scatterometer and altimeter data is supported by a similar rise in sea level observed from tide gauge measurements at two locations in New Zealand. The spatial correlation between the two satellite estimates of sea level change is about 0.5. This agreement suggests that time-dependent Sverdrup dynamics may account for about ¼ of the spatial variance of sea level change in the South Pacific over the 3-month Seasat mission.