Global Kilometer-Scale Simulations with ARP-GEM2: Effect of Parameterized Convection and Calibration

TL;DR

This paper presents the second version of the ARP-GEM global atmospheric model, calibrated at kilometer-scale resolution, and investigates the effects of parameterized convection on climate simulation accuracy at 2.6 km resolution.

Contribution

It introduces a calibrated, high-resolution global atmospheric model and analyzes the impact of parameterized convection on climate simulation fidelity.

Findings

Parameterized convection remains important at kilometer scale.

High resolution offers added value in climate variability representation.

A balance between mean state accuracy and variability is needed.

Abstract

The objective of this paper is twofold. First, it documents the second version of the global atmospheric model ARP-GEM and its calibration at kilometer-scale resolution. The model is currently able to run simulations at a resolution of up to 1.3 km. Second, this paper focus on multi-year global atmospheric simulations at a 2.6 km resolution with and without parameterized convection and associated calibration. Simulations without deep convection tend to be similar to those with infinite, or at least large, entrainment values. Consistently, entrainment and detrainment are used as primary drivers for the gradual reduction of convection as resolution increases. The results indicate that, with this hydrostatic model, parameterized convection still plays a significant role in the correct representation of the mean state at the kilometer scale. Additionally, they suggest some added value of high resolution in representing climate variability. However, a compromise between the adequate representation of the mean state and variability is necessary, as both are differently favored by the degree of parameterized convection. Finally, it is likely that even higher resolutions are necessary to achieve an unequivocal added value.