Eddy kinetic energy distribution in the Southern Ocean from altimetry and FGGE drifting buoys

Abstract

The eddy kinetic energy distribution in the Southern Ocean has been estimated from Seasat altimeter data available on repetitive orbits during 24 days in September–October 1978 and from 192 free‐drifting buoy trajectories obtained during the First GARP Global Experiment (FGGE) from November 1978 to the first months of 1980. A good spatial coherence is found between the results of these two independent methods in the Southern Ocean from 30°S to 65°S. The distribution shows strong, eddy kinetic activity near the western boundaries (Argentine Basin, Mozambique Plateau, Tasman Sea, etc.) and near topographic features (ridges and continental shelves: Drake Passage, Crozet and Kerguelen plateaus, Macquarie Rise, etc.). At first the ratio between both estimates was found to be very high, with kinetic energy distribution from FGGE drifters being 3 times larger than from the altimeter. After an investigation of the effect of the wind on eddy kinetic energy estimates from drifting buoys it seems that the wind cannot be the main reason for such a large discrepancy. Next, the eddy kinetic energy distribution from drifters was recomputed and processed through a band‐pass filter, in the range 1/6 to 1/24 cycles per day, in order to achieve a better match to the temporal scales explored by Seasat altimeter measurements. Although there still remain some differences between the two distributions, comparable values for mean eddy kinetic energy estimates over the whole Southern Ocean are then found. The remaining differences might be attributed to various sources, one of them being the nonsimultaneity of the two data bases.