Seasonal amplitude of principal tidal constituents in shallow shelf regions

Abstract

Understanding the seasonal variation (annual cycle) of tides is crucial for coastal management and the planning of coastal infrastructure, as well as pivotal for navigation safety, prediction of extreme sea levels and so on. Specifically, seasonal variations of M₂ amplitudes, larger in summer and smaller in winter, have attracted widespread attention. Nevertheless, investigations into other tidal constituents, such as S₂, K₁, O₁, remain comparatively sparse. Here, seasonal variations of the four principal tidal constituents are studied in the shallow shelf regions of the China Seas and the North Sea, both acknowledged for exhibiting the most pronounced seasonal modulations of M₂ amplitude, attributable to vertical stratification. We perform a segmented Harmonic Analysis with moving average filter, to remove semi-annual cycle, at 25 tide gauge data and find a synchronized seasonal modulation of M₂ and O₁ in China, which can be explained by stratification. Whereas S₂ manifest an inverse seasonal modulation, larger in winter and smaller in summer, attributed to the sun's varying proximity to the earth. The K₁ tide displays two very different seasonal cycle, also influenced by astronomical modulation. This observed pattern basically persists in the North Sea, while O₁ shows a negative seasonal amplitude but still exists high correlation coefficient with M₂. Consequently, this study provides a deep insight into 4 principal tidal constituents' seasonal modulation and underlying mechanisms, thereby enhancing our ability to comprehend and predict water level extremes and flooding with greater precision.