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Title : The atmospheric response to weak sea surface temperature fronts
Name of the speaker : Niklas Schneider
Affiliation : International Pacific Research Center and Department of Oceanography University of Hawaii
Laboratory organizer : LOCEAN
Date and time : 11-06-2014 15h00
Location : UPMC - LOCEAN - Tour 45-55, 4e ├ętage
Summary :

The response of the atmospheric boundary layer to fronts of sea surface temperature (SST) is characterized by reduction of wind speed over warm SST, and a tight correlation between curl and divergence of the wind stress and the down- and crosswind components of the SST gradient, respectively. The associated regression (or coupling) coefficients for the wind stress divergence are consistently larger than those for the wind stress curl. To explore the underlying physics we introduce a linear model of the atmospheric boundary response to SST fronts in the presence of background advection. The model includes modulation by gradients of SST of boundary layer hydrostatic pressure and vertical mixing, and of the impact of secondary circulation on stratification aloft of the boundary layer. The model solutions are a strong function of the scale of the SST and the background advection, and recover observed characteristics. The coupling coefficients for wind stress curl and divergence are governed by distinct physics. The latter is dominated by non-rotational sea-breeze, while the former is governed by geostrophic spin-down.