Dynamics of the Mediterranean salinity tongue

A reduced-gravity planetary-geostrophic model of the North Atlantic consist ing of two active layers overlying a motionless abyss is developed to inves tigate the effect of the wind field in shaping the dynamics of the Mediterr anean salinity tongue. The model is driven by climatological winds and east ern boundary ventilation in a basin of realistic geometry and includes a pa rameterization of meddles. The upper-layer depth from the model shows a clear similarity to observatio ns, both in terms of the location and intensity of the subtropical gyre and also the position of the outcropping line in the northern basin. Potential vorticity in layer two reproduces the sweep of potential-vorticity contour s southwestward from the eastern boundary and extending westward into the i nterior, and provides the pathways along which Mediterranean Water spreads into the model interior. The authors solve for the steady salinity field in the second layer, includ ing sources of Upper Labrador Sea Water and Antarctic Intermediate Water on the isopycnal surface. The shape and spreading latitude of the model salin ity tongues bear a striking resemblance to observations. Both the wind forc ing and the occurrence of a mean transport of Mediterranean Water away from the eastern boundary are crucial in obtaining a realistic salinity tongue. The salinity tongues are remarkably stable to variations in the Peclet num ber: A simple parameterization of meddles in the model is also included. Where m eddles are dissipated locally by collisions with topographic seamounts, for example, they may generate large recirculations extending across to the we stern boundary. The net effect of these recirculations is to shift the sali nity tongue equatorward.