44 Years Hindcast of the sea level and circulation in the Baltic Sea

The subject of the investigation was the multiyear hindcast of the sea level elevations and currents over the Baltic Sea. The approach follows to the HIPOCAS project conception and contained the 3D hydrodynamic model using boundary conditions from the atmosphere and catchment for 44-year period referring to the second half of the 20th century.The sea level fluctuations and current hindcast were performed by the M3D_UG model based on the POM. The evaluations of hindcast accuracy were done by comparison of the modelled simulations to field observations. Their results were presented as statistical measures cored on the mean and integral square errors. The model results compared to the observed data agreed well and confirmed usefullness of the used model for hindcast.Except for the hindcast quality evaluations, both observed and modelled sea level elevations were analyzed by the spectral and principal component analysis methods for singling out the components of its variability. The research proved at least two opposite trends — decreasing at the northern coast and increasing in the southern ones. Moreover, three temporal components of their variability were revealed. Due to vectorial and modular average of currents, annual circulation patterns in the Baltic Sea have been obtained. Using of long term sequences of the current fields, inter annual changes of averaged velocity and their increasing trend were evaluated.