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Ekman drift and vortical structures
Yves Morel, Leif Thomas
SHOM
(Abstract received 03/28/2009 for session X)
ABSTRACT
We have studied the influence of a constant wind on the displacement of a vortex. The well known Ekman current develops in the surface layer and is responsible for a transport perpendicular to the wind: the Ekman drift. An additional process is however evidenced, whose importance is as strong as the Ekman drift. There indeed exists a curl of the wind-driven acceleration along isopycnic surfaces when they are spatially variable (they enter and leave the depth where the wind stress acts), which generates potential vorticity anomalies. This diabatic effect is shown to generate potential vorticity anomalies which acts on the propagation of vortical waves and non linear vortices. It is shown that this effect drastically reduces the effect of the Ekman drift for linear waves and surface intensified vortices, while extending its effect to subsurface vortices. It also generates along wind propagation, whose sign depends on the vortex characteristics.
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2009 LOM Workshop, Miami, Florida Jume 1 - 3, 2009