Entrainment and mixing in a high-resolution large-eddy simulation of stratocumulus

DYCOMS-II was a field experiment designed to provide measurements of nocturnal stratocumulus-topped marine boundary layers for evaluating LES models. Aircraft flights through stratocumulus clouds during the DYCOMS-II study revealed narrow in-cloud regions with reduced liquid water content (LWC) and temperatures. These "cloud holes" were concentrated near cloud top, and their average width near cloud top was about 5 m (Gerber et al. 2005).

We compared the results of a high-resolution (5-m vertical and 6-m horizontal grid sizes) large-eddy simulation (LES) based on the 2nd research flight (RF02) of DYCOMS-II to aircraft measurements taken during a DYCOMS-II flight near cloud top. The comparisons used measurements and LES results at comparable spatial scales (10 m) and demonstrate that the LES is able to reproduce the key features of the observed distributions of conserved variables in the entrainment zone. The results suggest that high-resolution LES is able to resolve many aspects of the entrainment process in DYCOMS-II stratocumulus clouds.