Variable-resolution Mesh Experiments

Using the subgrid-scale parameterization of convection developed by Grell and Freitas (2014) and implemented in the Model for Prediction Across Scales (MPAS), MMM scientists analyzed the impact of horizontal mesh resolution on the simulation of monthly-mean precipitation rates over the Tropical Pacific Ocean for December 2015.

As shown in the figure below, the panels labelled GFu and GFu-DEEPC display the total and convective precipitation rates simulated with a 30 km uniform mesh. The panels labelled GFv and GFv-DEEPC display the total and convective precipitation rates simulated with a 30-6 km variable mesh centered along the Equator at 165ºW. The panels GFu-DEEPC and GFv-DEEPC highlight the impact of the scale-aware convection scheme on the convective precipitation. Over the refined area of the mesh, subgrid-scale convective precipitation decreases between GFu-DEEPC and GFv-DEEPC as convection becomes explicitly resolved. Outside the refined area of the mesh, subgrid-scale convective precipitation increases, as seen over the Tropical Eastern Pacific and West Pacific warm pool. The panels GFu and GFv reveal little differences in the total precipitation between the experiments using the uniform and variable resolution meshes, due to the compensation between grid-scale and convective precipitation as horizontal resolution increases. Comparing the GFu and GFv panels against the TMPA panel highlight biases in simulated precipitation against satellite-derived precipitation, most notably along the Eastern Tropical Pacific.

Comparing the GFu and GFv panels against the TMPA panel highlight biases in simulated precipitation against satellite-derived precipitation, most notably along the Eastern Tropical Pacific

Although numerical weather prediction aims at global convection-permitting scale modeling, variable-resolution mesh experiments are intermediate valuable tools to help improve convective parameterizations and their interactions with grid-scale microphysics at seasonal and sub-seasonal scales.