Shear-generating motions at various length scales and frequencies in the Baltic Sea - an attempt to narrow down the problem of horizontal dispersion

In the Baltic Proper, the mean circulation is too weak to explain the fast southward spreading of the so-called juvenile freshwater trapped by the seasonal thermocline in the summer season. Improved knowledge of the spatial and temporal scales of the velocity field is needed to better model dispersion. Spatial and temporal scales are investigated using some large historic data sets. Inertial oscillations are almost always present in the Baltic Proper, irrespective of wind conditions and mixed layer thicknesses. Analyses of the coherence in one data set reveal that the inertial oscillations have a horizontal coherence scale of 10-20 km under the conditions experienced during those measurements. Transient eddies and basin-scale modes with weaker periodicity are also indicated in our data sets. A tentative wavenumber spectrum is constructed for the Baltic Proper.