M. Keruss, J. Sennikovs
Laboratory for Mathematical Modelling of Environmental and Technological Processes, University of Latvia, Latvia, e-mail:jsenniko@latnet.lv
 

The water level fluctuations in the Baltic Sea are mainly caused by the meteorological forcing. High amplitudes of these fluctuations make evaluation of tidal amplitudes difficult. The main goal of this study is to find optimal filtering of water level time-series for the correct determination of the tidal characteristics.
An extensive set of the water elevation data from several gauging stations around the Latvian coast of the Baltic Sea and the Gulf of Riga has been analyzed. The temporal span of the data (25 years) allowed determination of the amplitudes of the main tidal constituents. The values of them are in the range from 4 to 8 centimeters. The spatial distribution of the gauging stations allowed estimation of the phases of tidal waves. Occasional measurements of the amplitudes of the internal tidal waves in the Gulf of Riga are found to be in agreement with the ones found from the determined surface tidal amplitudes.
The shallow water model has been employed as a tool for determination of the resonance frequencies of the Gulf of Riga. These frequencies are also found using spectral analysis of the elevation data. The results of the model runs are used as an additional estimator of the amplitudes of the tidal constituents.