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Title: Why do general circulation models overestimate the aerosol cloud lifetime effect? A case study comparing CAM5 and a CRM

Observation-based studies have shown that the aerosol cloud lifetime effect or the increase of cloud liquid water path (LWP) with increased aerosol loading may have been overestimated in climate models. Here, we simulate shallow warm clouds on 27 May 2011 at the southern Great Plains (SGP) measurement site established by the Department of Energy's (DOE) Atmospheric Radiation Measurement (ARM) program using a single-column version of a global climate model (Community Atmosphere Model or CAM) and a cloud resolving model (CRM). The LWP simulated by CAM increases substantially with aerosol loading while that in the CRM does not. The increase of LWP in CAM is caused by a large decrease of the autoconversion rate when cloud droplet number increases. In the CRM, the autoconversion rate is also reduced, but this is offset or even outweighed by the increased evaporation of cloud droplets near the cloud top, resulting in an overall decrease in LWP. Lastly, our results suggest that climate models need to include the dependence of cloud top growth and the evaporation/condensation process on cloud droplet number concentrations.
Authors:
 [1] ;  [1]
  1. Univ. of Michigan, Ann Arbor, MI (United States)
Publication Date:
Grant/Contract Number:
SC0008486; DOE DE-SC0008486
Type:
Published Article
Journal Name:
Atmospheric Chemistry and Physics (Online)
Additional Journal Information:
Journal Name: Atmospheric Chemistry and Physics (Online); Journal Volume: 17; Journal Issue: 1; Journal ID: ISSN 1680-7324
Publisher:
European Geosciences Union
Research Org:
Univ. of Michigan, Ann Arbor, MI (United States)
Sponsoring Org:
USDOE Office of Science (SC)
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES
OSTI Identifier:
1337795
Alternate Identifier(s):
OSTI ID: 1346036

Zhou, Cheng, and Penner, Joyce E. Why do general circulation models overestimate the aerosol cloud lifetime effect? A case study comparing CAM5 and a CRM. United States: N. p., Web. doi:10.5194/acp-17-21-2017.
Zhou, Cheng, & Penner, Joyce E. Why do general circulation models overestimate the aerosol cloud lifetime effect? A case study comparing CAM5 and a CRM. United States. doi:10.5194/acp-17-21-2017.
Zhou, Cheng, and Penner, Joyce E. 2017. "Why do general circulation models overestimate the aerosol cloud lifetime effect? A case study comparing CAM5 and a CRM". United States. doi:10.5194/acp-17-21-2017.
@article{osti_1337795,
title = {Why do general circulation models overestimate the aerosol cloud lifetime effect? A case study comparing CAM5 and a CRM},
author = {Zhou, Cheng and Penner, Joyce E.},
abstractNote = {Observation-based studies have shown that the aerosol cloud lifetime effect or the increase of cloud liquid water path (LWP) with increased aerosol loading may have been overestimated in climate models. Here, we simulate shallow warm clouds on 27 May 2011 at the southern Great Plains (SGP) measurement site established by the Department of Energy's (DOE) Atmospheric Radiation Measurement (ARM) program using a single-column version of a global climate model (Community Atmosphere Model or CAM) and a cloud resolving model (CRM). The LWP simulated by CAM increases substantially with aerosol loading while that in the CRM does not. The increase of LWP in CAM is caused by a large decrease of the autoconversion rate when cloud droplet number increases. In the CRM, the autoconversion rate is also reduced, but this is offset or even outweighed by the increased evaporation of cloud droplets near the cloud top, resulting in an overall decrease in LWP. Lastly, our results suggest that climate models need to include the dependence of cloud top growth and the evaporation/condensation process on cloud droplet number concentrations.},
doi = {10.5194/acp-17-21-2017},
journal = {Atmospheric Chemistry and Physics (Online)},
number = 1,
volume = 17,
place = {United States},
year = {2017},
month = {1}
}