Exploring the Impacts of Physics and Resolution on Aqua-Planet Simulations from a Non-Hydrostatic Global Variable-Resolution Modeling Framework
Limited by computing resources, global climate models are designed to simulate atmospheric processes at relatively coarse spatial resolution using a hydrostatic approximation that allows the models to run efficiently. A study, led by researchers at Pacific Northwest National Laboratory, investigated the use of a non-hydrostatic global model for climate modeling. Getting rid of the hydrostatic approximation, the model is suitable for very high resolution modeling. Applied to an all-water planet, the team explored how simulations from the non-hydrostatic model may be sensitive to model resolution and the representation of certain physical processes. The finding motivates future research to further investigate the use of the non-hydrostatic model for very high resolution climate modeling in which convection may be explicitly simulated in a refined region of the globe.
Atmospheric processes vary on a wide range of spatial scales, from clouds that cover a kilometer or less to frontal systems that cover hundreds of kilometers or more. As an atmospheric model grid cell becomes smaller, more processes are explicitly simulated. But for climate modeling, that requires long simulations—a challenging computational feat. High resolution modeling is more feasible in a global variable resolution modeling framework with a refined (high resolution) mesh applied only to specific regions. By testing a non-hydrostatic global variable resolution model in an all-water planet for climate simulations, this study establishes a baseline for future investigations of the modeling approach for very high resolution climate modeling.
Traditionally, atmospheric models use an approximation that the gravity and the vertical pressure gradient forces acting on an air parcel are in balance. This approximation allows atmospheric models to run efficiently but limits their applications to model grid sizes of a few 10s of kilometers or larger. Non-hydrostatic models that get rid of the hydrostatic approximation have been used in weather forecasting but few efforts have explored their use in climate modeling. The non-hydrostatic Model for Prediction Across Scales (NH-MPAS) is one of a few models that provide a global framework to achieve high resolution using regional mesh refinement. Previous research has demonstrated the use of the MPAS model in a hydrostatic configuration (H-MPAS). This study, led by researchers at Pacific Northwest National Laboratory, compares the sensitivity of NH-MPAS and H-MPAS to model resolution and physics representations, with a primary focus on the distinct characteristics of precipitation, clouds, and large-scale circulation simulated by the models. The NH-MPAS model exhibited reduced sensitivity compared to H-MPAS. This important feature may allow NH-MPAS to be applicable over a wider range of model resolution and suggests a potential for explicit simulation of convection regional refinement.