Environmental sensitivities of shallow-cumulus dilution. Part I: Selected thermodynamic conditions

doi:10.5194/acp-2020-336

GSTDTAP > 地球科学

DOI	10.5194/acp-2020-336
	Environmental sensitivities of shallow-cumulus dilution. Part I: Selected thermodynamic conditions
	Sonja Drueke, Daniel J. Kirshbaum, and Pavlos Kollias
	2020-04-29
发表期刊	Atmospheric Chemistry and Physics
出版年	2020
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 (m_b), driven by stronger surface heating and subcloud turbulence. As m_b increasies, 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 virtually no sensitivity to the former and only a 15 % reduction in dilution for a tripling of the latter (from 250 m to 750 m). 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.
领域	地球科学
URL	查看原文
引用统计
文献类型	期刊论文
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/248880
专题	地球科学
推荐引用方式 GB/T 7714	Sonja Drueke, Daniel J. Kirshbaum, and Pavlos Kollias. Environmental sensitivities of shallow-cumulus dilution. Part I: Selected thermodynamic conditions[J]. Atmospheric Chemistry and Physics,2020.
APA	Sonja Drueke, Daniel J. Kirshbaum, and Pavlos Kollias.(2020).Environmental sensitivities of shallow-cumulus dilution. Part I: Selected thermodynamic conditions.Atmospheric Chemistry and Physics.
MLA	Sonja Drueke, Daniel J. Kirshbaum, and Pavlos Kollias."Environmental sensitivities of shallow-cumulus dilution. Part I: Selected thermodynamic conditions".Atmospheric Chemistry and Physics (2020).