Numerical simulations of extratropical tropopause‐penetrating convection: Sensitivities to grid resolution

Abstract

AbstractDeep extratropical convection that penetrates and overshoots the altitude of the tropopause has important implications both for chemistry‐climate interactions through stratosphere‐troposphere exchange and for hazardous weather at the Earth's surface. In this study, the sensitivity of tropopause structure and cross‐tropopause transport to the choice of numerical model resolution in simulations with explicitly resolved convection (i.e., no convective parameterization) is examined. For an observed case of overshooting convection, the Advanced Research Weather Research and Forecasting (ARW‐WRF) model is run for all possible combinations of three horizontal (3 km, 1 km, and 333.33 m) and vertical (600 m, 300 m, and 150 m) grid resolutions. Although ARW‐WRF is successful in producing tropopause‐penetrating convection in each case, the depth of overshooting and cross‐tropopause transport are found to increase with refinement in the horizontal dimension and decrease with refinement in the vertical dimension. These results are related to changes in storm intensity and the sharpness of the tropopause, where the former is found to increase with refinement in the horizontal dimension and the latter is found to increase with refinement in the vertical dimension. Comparisons of simulated storm altitudes with those observed from ground‐based radar reveal large positive biases in simulations where the horizontal resolution is fine and the vertical resolution is coarse.