Eddy Variability and Energetics from Direct Current Measurements in the Antarctic Circumpolar Current South of Australia

Two year time series measurements of current velocity and temperature in the Subantarctic (SAF) south of Australia from 1993 to 1995 provide estimates of eddy fluxes of heat momentum across the Antarctic Circumpolar Current (ACC) and further insight into the of the ACC. The SAF was found to be an energetic, meandering jet with vertically fluctuations varying on a timescale of 20 days with typical amplitude 30 cm/s 1150 dbar. A daily-varying coordinate frame which follows the direction of ow allowed variability of the SAF to be isolated from variability due to meandering of the and proved very successful for examining eddy uxes. Vertically averaged cross-stream heat flux was 11.3 kW/m^2 poleward and significantly different from zero at the 95% interval for fluctuations in the 2-90 day band. Zonally integrated, this eddy heat (=0.9 PW) is more than large enough to balance heat lost south of the Polar Front is as large as cross-SAF fluxes found in Drake Passage. Cross-stream eddy momentum were small, not significantly different from zero and of indeterminate sign, but tending decelerate the mean flow. A relationship between vertical motion and meander phase in the Gulf Stream was found to hold for the SAF. Eddy kinetic energy levels were to those in Drake Passage and southeast of New Zealand. Eddy potential energy was to an order of magnitude larger than other ACC sites, most likely because meandering the front is more common here. Baroclinic conversion was found to be the dominant by which eddies grow south of Australia. Typical eddy growth rate is estimated be 30 days, approximately twice as fast as in Drake Passage, consistent with eddy energy rapidly downstream.