Shallow Cumulus in Single-Column WRF Simulations Evaluated with the LASSO Framework

Shallow cumulus is a challenge to mesoscale numerical weather prediction models. These cloud fields have important effects on temperature, solar irradiance, convective initiation, and pollutant transport, among others. Recent improvements to physics schemes available in the Weather Research and Forecasting model (WRF) aim to improve representation of shallow cumulus, in particular over land. The DOE LES ARM Symbiotic Simulation and Observation Workflow (LASSO) project provides several cases that we use here to test the new physics improvements. The LASSO cases use multiple analyses to drive Large Eddy Simulations (LES), and the LES output is easily compared to output from WRF single-column simulations driven with the same analyses. The new Mellor-Yamada Nakanishi and Niino (MYNN) Eddy Diffusivity Mass Flux (EDMF) boundary layer and shallow cloud scheme produces clouds with timing, liquid water path, and cloud fraction that agree well with LES over a wide range of those variables. Here we examine those variables and test the scheme’s sensitivity to perturbations of a few key parameters. We also discuss the challenges and uncertainties of single-column tests. The older, simpler Total Energy Mass Flux (TEMF) scheme is included as a baseline.