Model resolution dependence of convection initiation by orographically-induced thermal circulations

Thermally-driven circulations in mountainous terrain can play an essential role in the initiation of deep moist convection: They advect moisture at low levels and provide the necessary trigger mechanism to lift air parcels above the level of free convection.
Current limited-area numerical weather prediction models with a horizontal grid spacing of around 1 km may adequately resolve the larger-scale thermal circulations, namely, valley winds and plain-to-mountain winds, but not the small-scale slope winds. In addition, the planetary boundary-layer parametrizations typically employed in these models are based on the assumption of horizontally homogeneous and flat terrain and assume none of the turbulent boundary-layer eddies are explicitly resolved.
In this contribution, we investigate the problems that arise due to these deficiencies in the given context using idealized numerical simulations with the WRF model. We compare simulations at different horizontal resolutions in the turbulence gray zone with LES simulations. Previous idealized modeling studies have shown that simulations at kilometer-scale resolution may produce stronger moisture convergence due to thermally-driven circulations and thus earlier and more vigorous convection over the mountain ridges compared with an LES model.
We focus on strongly-inhibited initial conditions that lead to deep moist convection with a kilometer-scale but not with an LES model and investigate the reasons for the different convective behavior. The benefits of scale-adaptive boundary-layer schemes for the studied process are evaluated.