Scenario simulations of recent Baltic Sea inflows using the hydrodynamic transport model GETM

Abstract

The aim of the present study is to simulate larger salt water inflows from the North Sea into the Baltic Sea reaching the Gotland Deep with the GETM (http://getm.eu) hydrodynamical model. Specifically we want to test the influence of different model settings, different initial conditions and a variety of forcing conditions on the occurrences of salt water inflows.The model area covers the whole Baltic Sea and North Sea, therefore no prescribed sealevel forcing in the Kattegat area is applied. Initial conditions and 3D boundary conditions are derived from climatological data. The tidal forcing at the open boundaries in the English Channel and the open North Sea are constructed from 13 partial tides taken from the TOPEX/POSEIDON harmonical tide analysis. Relatively coarse meteorological forcing available from ECMWF re-analysis data was used and seems to be of sufficient spatial resolution in order to reproduce the main features of the inflow dynamics during recent years. For the river inflow we used climatological data for the 30 most important rivers within the model area. It can be demonstrated, that the basic dynamics of sea level variations in that area is already reproduced by forcing the model with such low resolution meteorological data (0.5deg*0.5deg). Also the main characteristics of bottom and surface salinity are most of the time simulated sufficiently well. Further we are able to show, that for the larger events the inflowing salt water from the Belt Sea is also progressing in the simulations until it reaches the Gotland Deep. Finally we compare the modeled scenarios of the 2002 and 2003 inflows with measured data. From that we try to identify the most important criteria that allow salt water inflows to occur and we try to better assess the range of uncertainty.