Estimation of convective entrainment properties from a cloud-resolving model simulation during TWP-ICE

TitleEstimation of convective entrainment properties from a cloud-resolving model simulation during TWP-ICE
Publication TypeJournal Article
Year of Publication2016
AuthorsZhang GJ, Wu X.Q, Zeng X.P, Mitovski T.
JournalClimate Dynamics
Volume47
Pagination2177-2192
Date Published2016/10
Type of ArticleArticle
ISBN Number0930-7575
Accession NumberWOS:000384549500010
Keywordsbulk properties; Climate sensitivity; Cloud resolving model simulation of convection; cycle; detrainment; diurnal; Entrainment rates; high-resolution simulation; large-scale; LES; mass-flux scheme; models; parameterization; phase-iii; shallow cumulus convection
Abstract

The fractional entrainment rate in convective clouds is an important parameter in current convective parameterization schemes of climate models. In this paper, it is estimated using a 1-km-resolution cloud-resolving model (CRM) simulation of convective clouds from TWP-ICE (the Tropical Warm Pool-International Cloud Experiment). The clouds are divided into different types, characterized by cloud-top heights. The entrainment rates and moist static energy that is entrained or detrained are determined by analyzing the budget of moist static energy for each cloud type. Results show that the entrained air is a mixture of approximately equal amount of cloud air and environmental air, and the detrained air is a mixture of similar to 80 % of cloud air and 20 % of the air with saturation moist static energy at the environmental temperature. After taking into account the difference in moist static energy between the entrained air and the mean environment, the estimated fractional entrainment rate is much larger than those used in current convective parameterization schemes. High-resolution (100 m) large-eddy simulation of TWP-ICE convection was also analyzed to support the CRM results. It is shown that the characteristics of entrainment rates estimated using both the high-resolution data and CRM-resolution coarse-grained data are similar. For each cloud category, the entrainment rate is high near cloud base and top, but low in the middle of clouds. The entrainment rates are best fitted to the inverse of in-cloud vertical velocity by a second order polynomial.

DOI10.1007/s00382-015-2957-7
Short TitleClim. Dyn.
Student Publication: 
No