Seasonal variability of radiation tide in Gulf of Riga

Abstract. Diurnal oscillations of water level in Gulf of Riga are considered. It was found that there is distinct daily pattern of diurnal oscillations in certain seasons. The role of sea breeze, gravitational tides and atmospheric pressure gradient are analysed. The interference of the first two effects provide the dominant role in diurnal oscillations. The effect of gravitational tides is described both with sole tidal forcing and also in real case with atmospheric forcing and stratification. The yearly variation of the declination of the Sun and stratification leads to seasonal intensification of gravitational tides in Gulf of Riga. Correlation between gravitational tide of the Sun with its radiation caused wind effects appears to be main driver of oscillations in Gulf of Riga. Daily variation of wind is primary source of S₁ tidal component with a water level maximum at 18:00 UTC in Gulf of Riga. Effect of solar radiation influences also K₁ and P₁ tidal components which are examined, too.