Document Type
Article
Publication Date
12-1-2015
Publication Title
Journal of Advances in Modeling Earth Systems
Abstract
Large-eddy simulation is used to study the sensitivity of trade wind cumulus clouds to perturbations in cloud droplet number concentrations. We find that the trade wind cumulus system approaches a radiative-convective equilibrium state, modified by net warming and drying from imposed large-scale advective forcing. The system requires several days to reach equilibrium when cooling rates are specified but much less time, and with less sensitivity to cloud droplet number density, when radiation depends realistically on the vertical distribution of water vapor. The transient behavior and the properties of the near-equilibrium cloud field depend on the microphysical state and therefore on the cloud droplet number density, here taken as a proxy for the ambient aerosol. The primary response of the cloud field to changes in the cloud droplet number density is deepening of the cloud layer. This deepening leads to a decrease in relative humidity and a faster evaporation of small clouds and cloud remnants constituting a negative lifetime effect. In the near-equilibrium regime, the decrease in cloud cover compensates much of the Twomey effect, i.e., the brightening of the clouds, and the overall aerosol effect on the albedo of the organized precipitating cumulus cloud field is small.
Repository Citation
Seifert, Axel; Heus, Thijs; Pincus, Robert; and Stevens, Bjorn, "Large-Eddy Simulation of The Transient and Near-Equilibrium Behavior of Precipitating Shallow Convection" (2015). Physics Faculty Publications. 219.
https://engagedscholarship.csuohio.edu/sciphysics_facpub/219
DOI
10.1002/2015MS000489
Version
Publisher's PDF
Publisher's Statement
Open Access
Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 International License.
Volume
7
Issue
4
Comments
R.P. was supported by the US National Science Foundation (award AGS 1138394).