A conservative, discontinuous Galerkin, tracer transport scheme using compatible finite elements

TL;DR

This paper presents a conservative, discontinuous Galerkin finite element scheme for tracer transport in geophysical models, ensuring mass conservation and non-negativity across different vertical placements of the mixing ratio.

Contribution

It introduces a new tracer transport scheme that conserves mass and maintains consistency using compatible finite elements and a limiter for non-negativity.

Findings

The scheme conserves tracer mass in test cases.

It accurately models moisture transport in dynamical core simulations.

The limiter ensures non-negative tracer concentrations.

Abstract

This paper outlines a conservative transport scheme for scalar tracers within a compatible finite element model for geophysical fluid equations. Instead of using the advective transport equation for a mixing ratio, a conservative transport equation is solved for the tracer density of the mixing ratio multiplied by the dry density. This ensures mass conservation in the continuous equations, which can be preserved in the discrete equations with a discontinuous Galerkin transport scheme. Our method is designed to work for two placements of the mixing ratio in a Charney-Phillips vertical staggering: either co-located with the dry density or vertically staggered from it. The new scheme is designed to conserve the tracer density and ensure consistency by maintaining a constant mixing ratio. Additionally, a mass-conserving limiter is developed to ensure non-negativity in the co-located configuration. Tests with terminator toy chemistry and a moist rising bubble show the use of the new transport scheme with physics terms and its ability to accurately model mass conservation of moisture species in a dynamical core setup.