Minimize Oceanic Eddies

Back to Oceanic Phenomena

Introduction

Since high-resolution images taken from satellites and space shuttles became available, oceanographers were quite surprised to learn that meso-scale and small-scale eddies or vortices are ubiquitous phenomena in coastal regions and at current fronts. Very spectacular images of small-scale eddies in coastal regions were acquired with a hand-held camera by the oceanographer-astronaut Scully-Power from the space shuttle Challenger during the Space Transportation System (STS) 41G mission in October 1984 (Scully-Power, 1986). However, such optical images can only be acquired during the day when there are no clouds and when the ocean is viewed at a favourable angle which is a function of the elevation and azimuth angle of the sun.

On the other hand, SAR can image eddies day and night and independent of cloud cover. Oceanic eddies become visible on optical and SAR images because the current field associated with the eddy modifies the sea surface roughness. The eddies become best visible on optical and radar images when the ocean surface is partially covered with surface films. These films are entrained by the flow associated with the eddy and accumulate in convergent regions where they reduce the sea surface roughness. Thus the surface films act as tracers for the flow field associated with the eddy. However, when the sea surface is completely covered with surface films, they lose their ability to trace the current field and the eddy becomes invisible.

Oceanic eddies can be generated by a variety of mechanism, e.g., (1) by local winds that are channeled by coastal geometry and topography, (2) by abrupt changes in wind speed and direction at atmospheric fronts, (3) by instabilities at oceanic current fronts, (4) by oceanic currents that interact with a headland, and (5) by water exchange through straits.

Vortex street generated in the laboratory

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