Fidelity of High-Order LES of Boundary Layer Clouds with Closed Entropy and Water Budgets

Abstract:

We recently developed a novel large eddy simulation (LES) infrastructure that uses specific entropy and total water specific humidity as prognostic thermodynamic variables and discretizes the equations of motion with high-order weighted essentially non-oscillatory (WENO) numerical schemes. Results of simulations of shallow cumulus and stratocumulus clouds across a range of resolutions show that high-order WENO schemes for scalars and momentum equations yield superior results to traditional central-difference schemes, even when the latter are of high order. The results are particularly striking for stratocumulus clouds, where high-order WENO schemes allow simulations to maintain stratocumulus clouds at appreciably lower resolution than central difference schemes, leading to net computational savings in using WENO schemes despite their computational overhead at fixed resolution. We propose a mechanism for the sensitivity of stratocumulus clouds to the numerical discretization.