Evaluation of tropical channel refinement using MPAS?￠????A aquaplanet simulations

摘要

Climate models with variable?￠????resolution grids offer a computationally less expensive way to provide more detailed information and increased accuracy by resolving processes that cannot be adequately represented by a coarser grid. This study uses the Model for Prediction Across Scales?￠????Atmosphere (MPAS?￠????A), consisting of a nonhydrostatic dynamical core and a subset of Weather Research and Forecasting (WRF) model physics, to investigate the potential benefits of using tropical channel refinement. The simulations are performed with an idealized aquaplanet configuration using 30 and 240 km global grid spacing, and two variable?￠????resolution grids spanning the same grid spacing range; one with a narrow (20???°S?￠????20???°N) and one with a wide (30???°S?￠????30???°N) tropical channel refinement. Increasing resolution in the tropics impacts both the tropical and extratropical circulation. Compared to the 30 km global grid, both refined channel simulations exhibit slightly stronger updrafts inside the Hadley cell resulting in more resolved precipitation. Using a wider tropical refinement leads to a closer correspondence with the global high?￠????resolution grid. While different grid spacings produce similar cloud size distributions that are consistent with observations, the dependence of precipitation rate on cloud size varies among simulations. The refined channel simulations show improved tropical and extratropical precipitation relative to the global coarse simulation. All simulations show a single precipitation peak centered on the equator. Although the results show that tropical refinement is an effective method for avoiding artifacts due to grid resolution sensitivities seen in earlier studies that only refined a portion of the tropics, some biases remain well inside of the refinement region.