Baroclinic Rossby radius of deformation in the southern Baltic Sea

The first baroclinic Rossby radius of deformation (R-1) is a fundamental horizontal scale of mesoscale processes. This scale is important for planning both numerical modelling and study areas. R-1 was computed on the basis of an 11-year series of high resolution CTD measurements collected during r/v 'Oceania' cruises. The data set covered the three main basins of the Baltic Proper: the Bornholm Basin (BB), the Slupsk Furrow (SF) and the Gdansk Basin (GB). The smallest mean value of R-1 was found in the Gdansk Basin (5.2 km), the largest one in the Bornholm Deep (7.3 km). The seasonal variability of R-1 is lower in the western basin than in the eastern one. The seasonal cycle of R-1 may be broken by extreme events, e.g. main Baltic inflows (MBI) of saline water. The inflowing water rebuilds the vertical stratification in the southern Baltic Sea and dramatically changes the R-1 values. The difference of R-1 between a stagnation period and an inflow situation is shown on the basis of observations made during 2002-2003. The main inflow occurred in winter, after ten years of stagnation, and the very low values of R-1 (about 4 km) changed to very high ones (more than 9 km). Analysis of stagnation and saltwater inflow events may throw light on the value of R-1 in future climatic scenarios. The potential influence of climate change on Baltic Sea salinity, especially a decrease in MBI activity, may change the baroclinic Rossby radius of deformation and the mesoscale dynamics. Values of R-1 are expected to be lower in the future climate than those measured nowadays.