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DOI	10.5194/acp-20-13217-2020
	Environmental sensitivities of shallow-cumulus dilution - Part 1: Selected thermodynamic conditions
	Drueke S.; Kirshbaum D.J.; Kollias P.
发表日期	2020
ISSN	16807316
起始页码	13217
结束页码	13239
卷号	20 期号:21
英文摘要	Cumulus entrainment, and its consequent dilution of buoyant cloud cores, strongly regulates the life cycle of shallow cumuli yet remains poorly understood. Herein, new insights into this problem are obtained through large-eddy simulations that systematically investigate the sensitivity of shallow-cumulus dilution to cloud-layer relative humidity (RH), cloud- and subcloud-layer depths, and continentality (i.e., the land-ocean contrast). The simulated cloud-core dilution is found to be strongly sensitive to continentality, with fractional dilution rates twice as large over the ocean as over land. Using a similarity theory based on the turbulent-kinetic-energy (TKE) budget, the reduced cloud-core dilution over land is attributed to larger cloud-base mass flux (mb), driven by stronger surface heating and subcloud turbulence. As mb increases, the fractional dilution rate must decrease to maintain energetic equilibrium. A positive sensitivity is also found to cloud-layer RH, with the core dilution increasing by 25 %-50 % for a 10 % enhancement in RH. This sensitivity is interpreted using the buoyancy-sorting hypothesis, in that mixtures of cloud and environmental air are more likely to become negatively buoyant and detrain (rather than diluting the cloud core) in drier cloud layers. By contrast, the sensitivities of (marine) shallow-cumulus dilution to cloud- and subcloud-layer depths are weak, with a 3 % decrease for a doubling for the former and a 4 % reduction in dilution for a 50 % deeper subcloud layer. These surprisingly weak sensitivities are readily explained by offsetting effects in the TKE similarity theory. Altogether, these experimental findings provide useful, though still incomplete, guidance for flow-dependent shallow-cumulus entrainment formulations in large-scale models. © Author(s) 2020. This work is distributed under the Creative Commons Attribution 4.0 License.
语种	英语
scopus关键词	buoyancy; cloud microphysics; cumulus; entrainment; kinetic energy; large eddy simulation; relative humidity; thermodynamics; turbulent flow
来源期刊	Atmospheric Chemistry and Physics
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/143829
作者单位	Department of Atmospheric and Oceanic Sciences, McGill University, Montréal, QC, Canada; School of Marine and Atmospheric Sciences, Stony Brook University, Stony Brook, NY, United States
推荐引用方式 GB/T 7714	Drueke S.,Kirshbaum D.J.,Kollias P.. Environmental sensitivities of shallow-cumulus dilution - Part 1: Selected thermodynamic conditions[J],2020,20(21).
APA	Drueke S.,Kirshbaum D.J.,&Kollias P..(2020).Environmental sensitivities of shallow-cumulus dilution - Part 1: Selected thermodynamic conditions.Atmospheric Chemistry and Physics,20(21).
MLA	Drueke S.,et al."Environmental sensitivities of shallow-cumulus dilution - Part 1: Selected thermodynamic conditions".Atmospheric Chemistry and Physics 20.21(2020).