Physics–Dynamics Coupling in Weather, Climate, and Earth System Models: Challenges and Recent Progress

Abstract

Numerical weather, climate, or Earth system models involve the coupling of components. At a broad level, these components can be classified as the resolved fluid dynamics, unresolved fluid dynamical aspects (i.e., those represented by physical parameterizations such as subgrid-scale mixing), and nonfluid dynamical aspects such as radiation and microphysical processes. Typically, each component is developed, at least initially, independently. Once development is mature, the components are coupled to deliver a model of the required complexity. The implementation of the coupling can have a significant impact on the model. As the error associated with each component decreases, the errors introduced by the coupling will eventually dominate. Hence, any improvement in one of the components is unlikely to improve the performance of the overall system. The challenges associated with combining the components to create a coherent model are here termed physics–dynamics coupling. The issue goes beyond the coupling between the parameterizations and the resolved fluid dynamics. This paper highlights recent progress and some of the current challenges. It focuses on three objectives: to illustrate the phenomenology of the coupling problem with references to examples in the literature, to show how the problem can be analyzed, and to create awareness of the issue across the disciplines and specializations. The topics addressed are different ways of advancing full models in time, approaches to understanding the role of the coupling and evaluation of approaches, coupling ocean and atmosphere models, thermodynamic compatibility between model components, and emerging issues such as those that arise as model resolutions increase and/or models use variable resolutions.

A Total Energy Error Analysis of Dynamical Cores and Physics‐Dynamics Coupling in the Community Atmosphere Model (CAM)

“…While it is advantageous to use state‐update PDC algorithm (ftype=1) in terms of having no spurious TE tendency from coupling, , it does result in spurious gravity waves in the simulations (see, e.g., Figure 5 in Gross et al, ). Figure a shows a 1‐year average of , a measure of high‐frequency gravity wave noise.…”

The coupling of deep convection with the resolved flow via the divergence of mass flux in the IFS

“…It will make their work more complex and also less flexible. But, in the long term, such a new way of thinking will have positive consequences in terms of consistency of the full system with respect to the original laws of fluid mechanics (Gross et al 2018). It is essential for resolution in the grey zone of key processes such as convection and turbulence, where the scale separation between resolved versus parametrized becomes fuzzy, and this work is a step forward in this respect.…”

A two‐fluid single‐column model of the dry, shear‐free, convective boundary layer

“…; Gross et al . ), Thuburn et al . () recently proposed an approach in which a full set of prognostic equations for density, momentum, potential temperature, and moisture is used for the resolved‐scale average dynamics of convective updaughts, as well as for their environment.…”