Cloud droplet sedimentation, entrainment efficiency, and subtropical stratocumulus albedo
TL;DR: In this article, the effect of cloud droplet sedimentation on the entrainment rate and liquid water path of a nocturnal nonsmoothing stratocumulus layer is examined using large-eddy simulations (LES) with bulk microphysics.
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Abstract: [1] The effect of cloud droplet sedimentation on the entrainment rate and liquid water path of a nocturnal nondrizzling stratocumulus layer is examined using large-eddy simulations (LES) with bulk microphysics. In agreement with a prior study by Ackerman et al. (2004), sedimentation is found to decrease entrainment rate and thereby increase liquid water path. They suggested this is due to reduction of boundary-layer turbulence. Our simulations suggest otherwise. Instead, sedimentation reduces entrainment by removing liquid water from the entrainment zone. This inhibits two mechanisms that promote the sinking of entrained air into the cloud layer–entrainment-induced evaporative cooling and longwave radiative cooling. A sensitivity study shows that the radiative effect is less important than the reduced evaporation. A possible parameterization of the effect of sedimentation on entrainment rate in a mixed layer model is proposed and tested. Since the droplet sedimentation rate is inversely related to cloud droplet (and presumably aerosol) concentration and nearly nondrizzling marine stratocumulus are widespread, sedimentation impacts on stratocumulus entrainment efficiency should be considered in climate model simulations of the aerosol indirect effect.
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Citations
Improving Stratocumulus Cloud Amounts in a 200‐m Resolution Multi‐Scale Modeling Framework Through Tuning of Its Interior Physics
Liran Peng,Peter N. Blossey,Walter M. Hannah,C. S. Bretherton,Christopher R. Terai,Andrea M. Jenney,Michael S. Pritchard +6 more
TL;DR: High-resolution multi-scale modeling frameworks produce biased low cloud amounts due to over-entrainment. This can be partly offset by using hyperviscosity and cloud droplet sedimentation.
Response to reviewers (acp-2022-583)
ARIUSNI LAIA
- 24 Feb 2023
TL;DR: In this article , the authors determine what causes the long-term trends in the shortwave (SW) top-of-the-atmosphere (TOA) fluxes over the North Atlantic region.
Comment on acp-2022-335
21 Jun 2022
TL;DR: In this article , the authors used satellite observations of the short-term development of clouds to examine the role of Nd perturbations in liquid water path (LWP) variations, suggesting an overall negative LWP response to Nd and a warming LWP adjustment to aerosol.
Reply to RC1
Edward Gryspeerdt
- 11 Aug 2022
TL;DR: In this paper , the authors used satellite observations of the short-term development of clouds to examine the role of Nd perturbations in liquid water path (LWP) variations, suggesting an overall negative LWP response to Nd and a warming LWP adjustment to aerosol.
Can GCMs represent cloud adjustments to aerosol–cloud interactions?
J. Mülmenstädt,Andrew S. Ackerman,Ann M. Fridlind,Meng Huang,Po‐Lun Ma,Naser G. A. Mahfouz,Susanne E. Bauer,Susannah M. Burrows,Matthew Christensen,Sudhakar Dipu,Andrew Gettelman,L. Ruby Leung,Florian Tornow,Johannes Quaas,Adam Varble,Hailong Wang,Kai Zhang,Youtong Zheng +17 more
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TL;DR: GCMs can represent cloud adjustments to aerosol–cloud interactions, but the modeled entrainment enhancement has a negligible global-mean effect.
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