Tides in Marginal, Semi-Enclosed and Coastal Seas - Part I: Sea Surface Height

5.11 Baltic Sea

The Baltic Sea is a rather shallow semi-enclosed sea with a very restricted access to the North Sea through the Kattegat. The tides as a consequence are rather small, a few cm at the most in most places. Figure 118 shows the bottom topography and the location of tidal stations. Figures 119 and 120 show the model results for the M2 and K1 tides. These should be compared to the results (Figure 121) presented by Dietrich et al (1980). Defant (1961) also presents some results for the M2 and K1 tides in the Baltic (Figure 122). Noticeably absent from Defant's results is the amphidrome in the northern Baltic, which is present in both our results and those of Dietrich et al. Overall, the model results are in good agreement with observations. Figure 123 shows the mixed nature of tides in the Baltic.

The semi-diurnal tides in the Baltic are described as two standing waves which have off-setting phases. These tides result from co-oscillating tides, from the North Sea through the Kattegat, and also from direct astronomical generation. However, the diurnal tides are generally regarded as primarily generated by astronomical forcing only. A significant amount of tidal energy is dissipated through the Kattegat Strait, especially for diurnal tides.

• Figure 118. The bottom topography of the Baltic Sea, with tide gage locations overlaid.
• Figure 119. The Baltic Sea M2 tide derived from the CU/NAVOCEANO model using data assimilation of tide gages.
• Baltic Sea M2 scatter plot of the model values versus tide gage observations, for model run with data assimilation of tide gages.
• The Baltic Sea S2 tide derived from the CU/NAVOCEANO model using data assimilation of tide gages.
• Baltic Sea S2 scatter plot of the model values versus tide gage observations, for model run with data assimilation of tide gages.
• The Baltic Sea N2 tide derived from the CU/NAVOCEANO model using data assimilation of tide gages.
• Baltic Sea N2 scatter plot of the model values versus tide gage observations, for model run with data assimilation of tide gages.
• The Baltic Sea K2 tide derived from the CU/NAVOCEANO model using data assimilation of tide gages.
• Baltic Sea K2 scatter plot of the model values versus tide gage observations, for model run with data assimilation of tide gages.
• Figure 120. The Baltic Sea K1 tide derived from the CU/NAVOCEANO model using data assimilation of tide gages.
• Baltic Sea K1 scatter plot of the model values versus tide gage observations, for model run with data assimilation of tide gages.
• The Baltic Sea O1 tide derived from the CU/NAVOCEANO model using data assimilation of tide gages.
• Baltic Sea O1 scatter plot of the model values versus tide gage observations, for model run with data assimilation of tide gages.
• The Baltic Sea P1 tide derived from the CU/NAVOCEANO model using data assimilation of tide gages.
• Baltic Sea P1 scatter plot of the model values versus tide gage observations, for model run with data assimilation of tide gages.
• The Baltic Sea Q1 tide derived from the CU/NAVOCEANO model using data assimilation of tide gages.
• Baltic Sea Q1 scatter plot of the model values versus tide gage observations, for model run with data assimilation of tide gages.
• Figure 121. The Baltic Sea (a) 2(M2+ S2 ) and the (b) 2(K1+O1) tidal range charts presented in Dietrich (1980). The M2 cophase contours have been overlaid in (a), and the K1 cophase contours have been overlaid in (b).
• Figure 122. The Baltic Sea M2 tide chart presented in Defant (1961).
• Figure 123. The nature of the Baltic Sea tides, derived from the CU/NAVOCEANO model: (M2+S2)/(K1+O1) ratio.

The animation clearly depicts the system of standing waves which characterize the Baltic Sea. High/low tide occurs at nearly the same time in the northern extreme as the southern extreme (centered around 15E, 55N), while the tides in the central basin (centered around 20E, 60N) are opposite (phase difference of nearly 180 degrees). The amphidromic point near 21E, 63.5N is evident, as the vector rapidly rotates clockwise in the animation.

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