Baroclinic adjustment in the Finnish coastal current

Abstract

Observations from the northern shore of the Gulf of Finland show a quasi-stable brackish coastal current flowing along a sloping bottom. Other examples of similar currents have been found, for example, in the Arctic basin. Generally, baroclinic flows of this type tend to be unstable. To study the stability of such flows, a specially designed numerical experiment has been devised. The simulations show that a current structure resembling that found in the observations results from an internal baroclinic adjustment of the flow to a baroclinically quasi-stable state with monotonic isopycnal vorticity. On the basis of the observations and numerical results, we propose that coastal currents for a certain part of the parameter range have an inherent tendency to evolve towards a quasi-stable state. This baroclinic neutralization is suggested as an explanation of the observed persistence of buoyant coastal currents under favorable conditions.