Numerical Simulations of Upper Troposphere/Lower Stratosphere (UTLS) Structure and Cross-Tropopause Transport in Deep Extratropical Convection: Sensitivities to Grid Resolution

Abstract:

Deep extratropical convection that overshoots the altitude of the tropopause is a process that has important implications both for chemistry-climate interactions through stratosphere-troposphere exchange and for hazardous weather at the Earth’s surface. Notably, convective injection of copious amounts of water vapor into the lower stratosphere has direct and significant impacts on the radiation budget and consequently, climate. In this study, the sensitivity of cross-tropopause transport and UTLS structure in extratropical convection to the choice of numerical model resolution in simulations of 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,333-m) and vertical (600-m,300-m,150-m) resolutions. Although the model is successful in simulating overshooting convection and cross-tropopause transport in each case, the depth and magnitude of troposphere-to-stratosphere transport is found to decrease with refinement in the vertical dimension and increase with refinement in the horizontal dimension. In addition, modifications to the altitude of the tropopause and the simulated depth of the convective storms show important sensitivities. Notably, the accuracy in the depth of the simulated storm is primarily dependent on vertical resolution. Recommendations for future modeling studies of extratropical convection and cross-tropopause transport will be given.