The role of sea surface temperatures in anchoring the Kuroshio and Gulf Stream Convergence Zones

Abstract:

Sea surface temperature fronts anchor surface wind convergences in regions of the Gulf Stream and Kuroshio Extension. We show that the observed characteristics of these Convergence Zones are captured by a boundary layer model that linearizes dynamics of the wind response to ocean-mesoscale sea surface temperatures about large-scale winds associated with the storm track. The model combines advection by large scale winds, rotation and accelerations due to sea surface temperature induced hydrostatic pressures and vertical mixing. When forced by idealized sea surface temperature fronts and observed probability density functions of large-scale winds, the model model reproduces i) the observed time-averaged wind divergence dipole with convergence (divergence) over warm (cool) waters that extend beyond the sharp sea surface temperature front, ii) the co-location away from the sea surface temperature front of wind divergence and Laplacian of air temperature, and iii) wind divergences (convergences) co-located with the sea surface temperature fronts when large-scale winds are aligned with (opposite to) sea surface temperature gradients and blow toward warm (cool) waters. This model reconciles on-going discussions of the dynamics governing these Convergence Zones.