Upscale Effects of Variable-Resolution Meshes on the Large-Scale Circulation

Friday, December 18, 2015 - 08:00
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Effects of regional grid refinement on the circulation outside the high-resolution domain (upscale effects) are investigated using the Model for Prediction Across Scales ­– Atmosphere (MPAS-A) hydrostatic dynamical core coupled to the physics parameterizations of the Community Atmosphere Model version 4. Previous studies using the same model in idealized experiments suggested upscale effects from the enhanced diabatic heating due to the resolution sensitivity of moist parameterizations and from the local enhancement of baroclinic eddies by the locally refined resolution. In this study, upscale effects are evaluated in an Atmospheric Model Intercomparison Project (AMIP)-type setting. Three variable-resolution simulations are contrasted to global quasi-uniform simulations. In the former, the global, quasi-uniform 120 km spacing mesh is locally refined to 30 km mesh inside a circular domain with 30° radius that are centered over North America (the Great Plains), South America (Amazon), and Asia (Tibetan Plateau), respectively. Compared to idealized experiments, the upscale effects in the AMIP simulations exhibit more complex spatial patterns and extend further away from the high-resolution regions. Notably the mid-latitude jet in the Southern Hemisphere is influenced in all the variable-resolution simulations, including the cases in which the grid refinement is confined in the Northern Hemisphere. The stationary waves emanating from the refined region to the Southern Hemisphere jet are further examined. Sensitivity of the upscale effects to the topography refinement is also discussed.