Coastal-trapped waves in elliptical lakes and around elliptical islands

Abstract

Abstract The propagation of low-frequency waves, trapped around the shelves of lakes and islands, is investigated. A two-layer model with a simple step topography is used to study the combined effects of depth changes and stratification. The lake or island boundary and corresponding shelf break are modelled as confocal ellipses and analytical solutions for the barotropic streamfunction, interface displacement and dispersion relation are found. Results show the presence of a topographically modified internal Kelvin wave and a stratification-modified topographic Rossby wave. The model is applied to the small, elongated northern basin of Lake Lugano. Although the Rossby wave frequency is close to its barotropic value the two mode 1 dispersion curves “kiss” for very weak stratification with important effects on the wave structures and velocities. The velocity field of the observed 74th oscillation more closely resembles that of an internal Kelvin wave than a topographic Rossby wave.