Seuren, Fleur ; Blume, Catherine ; Triana, Santiago Andrés ; Rekier, Jérémy

Poster presented at AGU Fall Meeting, San Francisco, Verenigde Staten on 2023-12-12

Abstract: Rossby waves, otherwise known as planetary waves or r-modes, are a common occurrence in rotating fluid systems, characterized by the conservation of absolute vorticity. In very thin spherical shells their frequencies are to a very good approximation given by the classic 2D dispersion relation but this approximation fails in thicker shells as the frequencies of tesseral Rossby modes tend towards zero when the shell width increases; giving the impression that there are no tesseral-like Rossby modes to be found in the full sphere. Here we show, using a simple numerical model, that we can retain the 2D approximation even in the full sphere by including a region of strong stable stratification that effectively replaces the inner boundary. In such a stably stratified sphere we recover the tesseral-like Rossby modes and, unlike in the thin spherical shell, several overtones with slightly smaller frequencies, representing tesseral-like Rossby modes that are dominant on different radii. Furthermore we demonstrate a relation between the shell width, stratification strength and frequency of the Rossby modes and their overtones offering a possible different method to probe rotating fluid systems.

Funding: H2020/855677/GRACEFUL