- Three mechanisms for self-induced Ekman pumping in the interiors of mesoscale ocean eddies are investigated.
The first arises from the surface stress that occurs because of differences between surface wind and
ocean velocities, resulting in Ekman upwelling and downwelling in the cores of anticyclones and cyclones,
respectively. The second mechanism arises from the interaction of the surface stress with the surface current
vorticity gradient, resulting in dipoles of Ekman upwelling and downwelling. The third mechanism arises from
eddy-induced spatial variability of sea surface temperature (SST), which generates a curl of the stress and
therefore Ekman pumping in regions of crosswind SST gradients. The spatial structures and relative magnitudes
of the three contributions to eddy-induced Ekman pumping are investigated by collocating satellite-based
measurements of SST, geostrophic velocity, and surface winds to the interiors of eddies identified
from their sea surface height signatures. On average, eddy-induced Ekman pumping velocities approach
O(10) cm day⁻¹. SST-induced Ekman pumping is usually secondary to the two current-induced mechanisms
for Ekman pumping. Notable exceptions are the midlatitude extensions of western boundary currents and the
Antarctic Circumpolar Current, where SST gradients are strong and all three mechanisms for eddy-induced
Ekman pumping are comparable in magnitude. Because the polarity of current-induced curl of the surface
stress opposes that of the eddy, the associated Ekman pumping attenuates the eddies. The decay time scale of
this attenuation is proportional to the vertical scale of the eddy and inversely proportional to the wind speed.
For typical values of these parameters, the decay time scale is about 1.3 yr.
- Gaube, P., Chelton, D. B., Samelson, R. M., Schlax, M. G., & O’Neill, L. W. (2015). Satellite Observations of Mesoscale Eddy-Induced Ekman Pumping. Journal of Physical Oceanography, 45(1), 104-132. doi:10.1175/JPO-D-14-0032.1
|Funding Statement (additional comments about funding)
- This work was
funded by NASA Grants NNX08AI80G, NNX08AR37G,
NNX13AD78G, NNX10AE91G, NNX13AE47G, and