A Comparison of Mesh Refinement in the Global MPAS-A and WRF Models Using an Idealized Normal-Mode Baroclinic Wave Simulation

Idealized normal-mode baroclinic wave simulations are conducted to examine the impact of continuous mesh refinement compared with stepwise changes in resolution using nested grids. The nested-grid results are produced using the Advanced Research Weather Research and Forecasting (VVRF-ARW) Model, hereafter ARW, and the continuous refinement results are produced using the atmospheric component of the Model for Prediction Across Scales-Atmosphere (MPAS-A). For the nested domain simulations with the ARW, variants of both one-way and two-way nesting techniques are examined. Significant reflection and distortion of waves are evident in results using one-way nesting, with the error increasing with decreasing boundary-update frequency. With continuous updating of the boundary conditions in one-way and two-way nesting, wave distortion is still evident near the lateral boundaries but the distortion is much less than with infrequent boundary updates. The conformal Voronoi meshes in MPAS provide a much smoother transition between mesh resolutions. Variable-resolution mesh MPAS-A simulations, using different transition zones between high- and low-resolution regions, are compared with the results from the ARW simulations. In the MPAS-A simulations, there is no significant reflection of gravity waves, suggesting that continuous mesh refinement can eliminate distortions that tend to occur along the boundaries of nested meshes.