# An explicit method to determine Casimirs in 2D geophysical flows

## TL;DR

This paper presents a method to explicitly construct Casimirs, which are conserved quantities, for 2D geophysical flows by rewriting the Poisson bracket in vorticity-divergence coordinates, enhancing understanding of flow structure.

## Contribution

The paper introduces a novel explicit method to determine Casimirs in 2D geophysical flows through coordinate transformation, improving upon heuristic approaches.

## Key findings

- Explicit construction of Casimirs in vorticity-divergence coordinates
- Provides a systematic way to identify conserved quantities
- Enhances understanding of geometric structure in geophysical flows

## Abstract

Conserved quantities in geophysical flows play an important role in the characterisation of geophysical dynamics and aid the development of structure-preserving numerical methods. A significant family of conserved quantities is formed by the Casimirs i.e., integral conservation laws that are in the kernel of the underlying Poisson bracket. The Casimirs hence determine the geometric structure of the geophysical fluid equations among which the enstrophy is well known. Often Casimirs are proposed on heuristic grounds and later verified to be part of the kernel of the Poisson bracket. In this work, we will explicitly construct Casimirs by rewriting the Poisson bracket in vorticity-divergence coordinates thereby providing explicit construction of Casimirs for 2D geophysical flow dynamics.