Second- and third-order vertical velocity budgets in cloudy boundary layers

Exact numerical budgets of second- and third-order vertical velocity moments were derived from large eddy simulations using the Naval Research Laboratory's COAMPS-LES model. Results from two different boundary layer cloud regimes are presented. The first one is a stratocumulus case and the second is a trade wind cumulus case.

Budgets of the vertical velocity variance have been studied quite extensively in previous studies, but third-order budgets have comparatively received little attention. Whereas the vertical velocity variance gives a broad measure of the strength of the turbulence, the third-order reveals more details about the organization of the turbulence, in particular the symmetry - or asymmetry - between updrafts and downdrafts.

Analysis of the third-order vertical velocity budget reveals interesting differences between the various cloud regimes simulated. In particular, the buoyancy is shown to play a large role in controlling the vertical velocity skewness.