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1
Ocean Fronts Impact Atmospheric Ekman Layer
N. Schneider1,2, B. Qiu2, Y. N. Sasaki1, A.
Lauer1, D.Stammer3 1IPRC, 2Dept. of Oceanography,
University of Hawaii, 3University of Hamburg,
Germany
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Winter 2008 wind stress curl (a) from the ECMWF
reanalysis and (b) reconstruction using
contributions from the sea level pressure
gradients, thermal wind, and spatially varying
eddy coefficients ( in 10-7Nm-3).
Normalized damping rate of relative vorticity
The effect of sea surface temperature (SST) on
the overlying atmospheric Ekman layer reflects a
significant ocean-to-atmosphere coupling
mechanism in the extratropics. The ECMWF analyses
(far left panel) shows the surface wind stress
curl during winter over the Gulf Stream. The
large values over regions of strong SST gradient
are apparent. The impact of the front on
different components of the Ekman layer were
analyzed and reconstructed statistically (middle
panel). The most important components in the
reconstruction are surface pressure gradients and
thermal wind spatial variation of boundary layer
eddy viscosity contributes less. The far right
panel shows the impact of the Ekman circulation
on atmospheric relative vorticity spindown.
Plotted are damping rates at each location
normalized by a value at a location distant from
the strong SST front. This damping of
tropospheric relative vorticity by up to 30 can
be expected to impact significantly the free
troposphere.