Casimir-dissipation stabilized stochastic rotating shallow water equations on the sphere

TL;DR

This paper presents a structure-preserving discretization method for stochastic rotating shallow water equations on the sphere, utilizing Casimir dissipation to stabilize simulations while conserving energy, and compares it to traditional Laplacian diffusion.

Contribution

It introduces a novel Casimir dissipation stabilization technique that preserves energy in stochastic shallow water models, improving stability and dynamic fidelity over standard methods.

Findings

Casimir dissipation stabilizes stochastic shallow water simulations.

The method preserves energy and enhances dynamic richness.

Compared to Laplacian diffusion, Casimir dissipation yields more stable and accurate results.

Abstract

We introduce a structure preserving discretization of stochastic rotating shallow water equations, stabilized with an energy conserving Casimir (i.e. potential enstrophy) dissipation. A stabilization of a stochastic scheme is usually required as, by modeling subgrid effects via stochastic processes, small scale features are injected which often lead to noise on the grid scale and numerical instability. Such noise is usually dissipated with a standard diffusion via a Laplacian which necessarily also dissipates energy. In this contribution we study the effects of using an energy preserving selective Casimir dissipation method compared to diffusion via a Laplacian. For both, we analyze stability and accuracy of the stochastic scheme. The results for a test case of a barotropically unstable jet show that Casimir dissipation allows for stable simulations that preserve energy and exhibit more dynamics than comparable runs that use a Laplacian.