Improving parameterization of entrainment rate for shallow convection with aircraft measurements and large-eddy simulation

TitleImproving parameterization of entrainment rate for shallow convection with aircraft measurements and large-eddy simulation
Publication TypeJournal Article
Year of Publication2016
AuthorsLu C.S, Liu Y.G, Zhang GJ, Wu X.H, Endo S., Cao L., Li Y.Q, Guo X.H
JournalJournal of the Atmospheric Sciences
Volume73
Pagination761-773
Date Published2016/02
Type of ArticleArticle
ISBN Number0022-4928
Accession NumberWOS:000373024700017
Keywordsbudget; Clouds; cycle; detrainment; diode-laser hygrometer; diurnal; microphysics; plume; resolving model; system; trade-wind cumulus
Abstract

This work examines the relationships of entrainment rate to vertical velocity, buoyancy, and turbulent dissipation rate by applying stepwise principal component regression to observational data from shallow cumulus clouds collected during the Routine Atmospheric Radiation Measurement (ARM) Aerial Facility (AAF) Clouds with Low Optical Water Depths (CLOWD) Optical Radiative Observations (RACORO) field campaign over the ARM Southern Great Plains (SGP) site near Lamont, Oklahoma. The cumulus clouds during the RACORO campaign simulated using a large-eddy simulation (LES) model are also examined with the same approach. The analysis shows that a combination of multiple variables can better represent entrainment rate in both the observations and LES than any single-variable fitting. Three commonly used parameterizations are also tested on the individual cloud scale. A new parameterization is thus presented that relates entrainment rate to vertical velocity, buoyancy, and dissipation rate; the effects of treating clouds as ensembles and humid shells surrounding cumulus clouds on the new parameterization are discussed. Physical mechanisms underlying the relationships of entrainment rate to vertical velocity, buoyancy, and dissipation rate are also explored.

DOI10.1175/jas-d-15-0050.1
Student Publication: 
No