Generation of mesoscale cyclonic eddies in the Baltic Sea with inflow events

A sigma-coordinate ocean model, by Blumberg and Mellor (POM). is applied to study the formation processes of mesoscale cyclones observed in the Baltic Sea, following the inflow events. The initial conditions simulate a situation when the Arkona and Bomholm Basins (or Arkona Basin solely) are already filled with the inflow water of the North Sea origin. while the rest of the sea still contains the old water of pre-inflow stratification. The model runs with constant and time dependent northerly/easterly wind, changing the buoyancy forcing, grid geometry and bottom topography, display the following. Entering the East Gotland Basin from the Slupsk Furrow. the bottom intrusion of saline inflow water splits in two: one goes northeast towards the Gotland Deep and the second moves southeast towards the Gulf of Gdansk. An intensive mesoscale cyclonic eddy carrying the inflow water is generated just east of the Slupsk Furrow with the inflow pulse. A number of smaller cyclones, with boluses of the inflow water, form in the intermediate layer along the saline intrusion pathway to the Gotland Deep. A similar cyclonic eddy is generated in the Bomholm Basin with the inflow pulse from the Arkona Basin. Following Spall and Price [19}, the cyclones are expected to form by the geostrophic adjustment of high potential vorticity inflow water column to a low potential vorticity environment. Some evidence for the PV outflow/inflow hypothesis is obtained in a numerical experiment, with a virtual dam restricting water exchange between the Bomholm and Gotland Basins to the limits of the Słupsk Furrow.