Direct Estimate of Lateral Eddy Diffusivity Upstream of Drake Passage

作者：Tulloch Ross; Ferrari Raffaele^*; Jahn Oliver; Klocker Andreas; LaCasce Joseph; Ledwell James R; Marshall John; Messias Marie Jose; Speer Kevin; Watson Andrew

来源：Journal of Physical Oceanography, 2014, 44(10): 2593-2616.

DOI：10.1175/JPO-D-13-0120.1

The first direct estimate of the rate at which geostrophic turbulence mixes tracers across the Antarctic Circumpolar Current is presented. The estimate is computed from the spreading of a tracer released upstream of Drake Passage as part of the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES). The meridional eddy diffusivity, a measure of the rate at which the area of the tracer spreads along an isopycnal across the Antarctic Circumpolar Current, is 710 +/- 260 m(2) s(-1) 1500-m depth. The estimate is based on an extrapolation of the tracer-based diffusivity using output from numerical tracers released in a one-twentieth of a degree model simulation of the circulation and turbulence in the Drake Passage region. The model is shown to reproduce the observed spreading rate of the DIMES tracer and suggests that the meridional eddy diffusivity is weak in the upper kilometer of the water column with values below 500 m(2) s(-1) a nd peaks at the steering level, near 2 km, where the eddy phase speed is equal to the mean flow speed. These vertical variations are not captured by ocean models presently used for climate studies, but they significantly affect the ventilation of different water masses.

• 出版日期2014-10