The Influence of Vertical Advection Discretization in WRF-ARW Model on Capping Inversion Representation in Warm-Season, Thunderstorm Supporting Environments

Abstract

This study evaluates forecasts of capping inversions and thermodynamic variables for believed areas of possible deep, moist convection initiation during the warm-season using the Weather Research and Forecasting Model (WRF) with the Advanced Research core (WRF-ARW). WRF-ARW was configured nearly identical to the National Severe Storms Laboratory (NSSL) version of WRF (NSSL-WRF). WRF-ARW's default third-order-accurate vertical advection scheme, which is an odd-order-accurate scheme, is known to introduce implicit damping which acts to dampen short wavelength features (Skamarock et al. 2008), such as capping inversions. It is hypothesized that by increasing WRF-ARW's vertical advection to the next higher, even-order-accurate vertical advection scheme, this would remove the associated implicit dampening, thus improving WRF-ARW's handling of capping inversion representation. After computing Student's t tests on the bias of each weather and thermodynamic variable, it was deemed that the fourth-order-accurate vertical advection scheme did not improve WRF-ARW's representation of capping inversion or other thermodynamic variables. Despite the rejected hypothesis, this study does confirm that the Mellor-Yamada-Janjić (MYJ) planetary boundary layer (PBL) parametrization has a cool and moist bias near the surface, as also found by Coniglio et al. (2013), Burlingame et al. (2017), Cohen et al. (2015) , Clark et al. (2012), among others. It is likely that the poor representation of capping inversions in WRF-ARW is from other numerics in the model, which is beyond the scope of this study.