![]() Furthermore, it became interesting to compare the tidal character and generation mechanism in the Baltic Sea with those in two other large European inland seas: the Black and Caspian. In the last three years, the authors were able to collect a large amount of additional tide gauge data for the Baltic Sea, allowing more detailed study. High-resolution spectral analysis revealed fine structure of tidal harmonics exceeding the noise level. ![]() (2013) used multi-year (5–31 years) hourly data-sets from 35 tide gauge stations to examine tidal oscillations in the Baltic Sea. Long time series of high-quality observations are necessary to precisely estimate tidal constituents in these seas. The accuracy of these calculations is limited because of the small tidal signal in comparison with the background noise level (s/n ratio). Studies of tides in these seas are based on relatively short series of tide gauge data (≤1 year). Tides in the Caspian Sea have been examined very little and mainly as part of more general investigations of sea level oscillations in this basin (cf. Tidal oscillations in the Baltic Sea and in the Black Sea have been studied for over 100 years, but the nature of their anomalous features is still not sufficiently clear ( Defant, 1961 Engel, 1974). The mechanism responsible for the formation of tides in these seas is in many ways similar to the mechanism of formation of eigen sea modes (seiches) and storm surges, in particular, the destructive surges in the Gulf of Finland, the Baltic Sea ( Kulikov and Medvedev, 2013). Tides produce regular periodic oscillations of sea level and currents other processes superimpose the tidal background. The Caspian Sea is the largest entirely enclosed inland body of water on the Earth consequently, only directly forced tides are formed in this sea.ĭespite their small amplitudes, tides in all these seas are scientifically interesting and important their accurate assessment is crucial for the understanding of the overall dynamics of the respective basins. Tides from neighboring basins have small influence on tidal oscillations in these seas. The Black Sea has limited water exchange with the Mediterranean Sea through the Turkish Straits (the Bosporus, the Sea of Marmara, and the Dardanelles). The Baltic Sea is a large enclosed shallow sea connected to the North Sea through the narrow and shallow Danish straits. Into isolated inland seas, such as the Black, Caspian and Baltic seas, oceanic tides penetrate weakly, or do not penetrate at all. Maximum amplitudes of tides are mainly observed in coastal waters of certain marginal seas. Tides are the major type of sea level oscillations in the world oceans. Maximum tidal heights estimated for a 100-year period are 23 cm in the Baltic Sea, 18 cm in the Black Sea and 21 cm in the southern Caspian Sea. ![]() The predominance of semidiurnal tides in the Caspian Sea has also probably a resonant nature. In the Black Sea amplification of semidiurnal tides is observed in the northwestern part, and is likely associated with local resonance. Thus, in the Baltic Sea with fundamental eigen period of about 27 h, diurnal tides dominate in the major eastern gulfs. ![]() Our findings indicate that the formation and predominance of diurnal or semidiurnal tides in these seas appears to depend on the frequency-selective properties of the basins. Harmonic analysis of tides for individual yearly series with consecutive vector averaging over the entire observational period was applied to estimate mean amplitudes and phases of tidal constituents. The diurnal radiational constituent S 1 (1 cpd), apparently associated with breeze winds, was found to play an important role in general tidal dynamics in these seas. High-resolution spectra revealed fine structure of discrete peaks at tidal frequencies. Long observation time series (up to 123 years in the Baltic Sea and 38 years in the Black and Caspian seas) at numerous stations were used to precisely estimate tidal constituents. Consequently, only directly forced tides are formed in these basins. However, oceanic tides penetrate weakly, or do not penetrate at all, into enclosed basins such as the Baltic, Black, and Caspian seas. Tides are the main type of sea level variability in the world oceans. 3Department of Fisheries and Oceans, Institute of Ocean Sciences, Sidney, BC, Canada.2Roshydromet, Fedorov Institute of Applied Geophysics, Moscow, Russia.Shirshov Institute of Oceanology, Russian Academy of Sciences, Moscow, Russia
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