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Title: Low‐Cloud Feedback in CAM5‐CLUBB: Physical Mechanisms and Parameter Sensitivity Analysis

Abstract

The physical mechanism of low-cloud feedbacks is examined by using perturbed-parameter ensemble (PPE) experiments in a unified scheme of boundary layer turbulence and shallow convection, named Cloud Layers Unified by Binormals (CLUBB) coupled to Community Atmosphere Model version 5 (CAM5). The shortwave cloud feedbacks in CAM5-CLUBB are positive in the most stable tropical regime, which is related to the weaker turbulence in the planetary boundary layer (PBL) in a warmer climate that is possibly triggered by the strengthened stability of the cloud layer. The positive feedback between low cloud cover (LCC), cloud top radiative cooling and PBL turbulent mixing may further enhance the decrease in LCC. The stronger inversion stability of PBL partly counters the decrease in LCC, and a recently developed index, the estimated cloud-top entrainment index (ECTEI), is a better predictor for LCC changes than conventional stability indices. The relative strength of shallow convection increases in the warmer climate, but its effect on low-cloud feedback is complicated by the unified treatment of shallow convection and PBL turbulence in CLUBB. Stronger shallow convection means more convective drying, but also less PBL turbulence and less LCC in the present climate, which leads to less reduction in LCC. The parameters relatedmore » to dynamic turbulent structure and double Gaussian closure in CLUBB are the most influential parameters on low-cloud feedbacks. Our results suggest that a unified treatment of shallow convection and turbulence may give rise to the predominate role of the PBL turbulent mixing in determining low-cloud feedback.« less

Authors:
ORCiD logo [1]; ORCiD logo [1];  [2];  [1]; ORCiD logo [2]; ORCiD logo [3]; ORCiD logo [4]; ORCiD logo [3]; ORCiD logo [3];  [5]; ORCiD logo [6]
  1. School of Atmospheric SciencesNanjing University Nanjing China; Joint International Research Laboratory of Atmospheric and Earth System Sciences &, Institute for Climate and Global Change ResearchNanjing University Nanjing China
  2. State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid DynamicsInstitute of Atmospheric Physics, Chinese Academy of Sciences Beijing China
  3. Pacific Northwest National Laboratory Richland WA USA
  4. Department of Mathematical SciencesUniversity of Wisconsin‐Milwaukee Milwaukee WI USA
  5. Lawrence Livermore National Laboratory Livermore CA USA
  6. National Center for Atmospheric Research Boulder CO USA
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1496795
Report Number(s):
PNNL-SA-139280
Journal ID: ISSN 1942-2466
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Journal Name:
Journal of Advances in Modeling Earth Systems
Additional Journal Information:
Journal Volume: 10; Journal Issue: 11; Journal ID: ISSN 1942-2466
Publisher:
American Geophysical Union (AGU)
Country of Publication:
United States
Language:
English
Subject:
CAM5, Cloud Layers Unified by Binormals (CLUBB)

Citation Formats

Zhang, Haipeng, Wang, Minghuai, Guo, Zhun, Zhou, Chen, Zhou, Tianjun, Qian, Yun, Larson, Vincent E., Ghan, Steven, Ovchinnikov, Mikhail, Bogenschutz, Peter A., and Gettelman, Andrew. Low‐Cloud Feedback in CAM5‐CLUBB: Physical Mechanisms and Parameter Sensitivity Analysis. United States: N. p., 2018. Web. doi:10.1029/2018MS001423.
Zhang, Haipeng, Wang, Minghuai, Guo, Zhun, Zhou, Chen, Zhou, Tianjun, Qian, Yun, Larson, Vincent E., Ghan, Steven, Ovchinnikov, Mikhail, Bogenschutz, Peter A., & Gettelman, Andrew. Low‐Cloud Feedback in CAM5‐CLUBB: Physical Mechanisms and Parameter Sensitivity Analysis. United States. doi:10.1029/2018MS001423.
Zhang, Haipeng, Wang, Minghuai, Guo, Zhun, Zhou, Chen, Zhou, Tianjun, Qian, Yun, Larson, Vincent E., Ghan, Steven, Ovchinnikov, Mikhail, Bogenschutz, Peter A., and Gettelman, Andrew. Thu . "Low‐Cloud Feedback in CAM5‐CLUBB: Physical Mechanisms and Parameter Sensitivity Analysis". United States. doi:10.1029/2018MS001423.
@article{osti_1496795,
title = {Low‐Cloud Feedback in CAM5‐CLUBB: Physical Mechanisms and Parameter Sensitivity Analysis},
author = {Zhang, Haipeng and Wang, Minghuai and Guo, Zhun and Zhou, Chen and Zhou, Tianjun and Qian, Yun and Larson, Vincent E. and Ghan, Steven and Ovchinnikov, Mikhail and Bogenschutz, Peter A. and Gettelman, Andrew},
abstractNote = {The physical mechanism of low-cloud feedbacks is examined by using perturbed-parameter ensemble (PPE) experiments in a unified scheme of boundary layer turbulence and shallow convection, named Cloud Layers Unified by Binormals (CLUBB) coupled to Community Atmosphere Model version 5 (CAM5). The shortwave cloud feedbacks in CAM5-CLUBB are positive in the most stable tropical regime, which is related to the weaker turbulence in the planetary boundary layer (PBL) in a warmer climate that is possibly triggered by the strengthened stability of the cloud layer. The positive feedback between low cloud cover (LCC), cloud top radiative cooling and PBL turbulent mixing may further enhance the decrease in LCC. The stronger inversion stability of PBL partly counters the decrease in LCC, and a recently developed index, the estimated cloud-top entrainment index (ECTEI), is a better predictor for LCC changes than conventional stability indices. The relative strength of shallow convection increases in the warmer climate, but its effect on low-cloud feedback is complicated by the unified treatment of shallow convection and PBL turbulence in CLUBB. Stronger shallow convection means more convective drying, but also less PBL turbulence and less LCC in the present climate, which leads to less reduction in LCC. The parameters related to dynamic turbulent structure and double Gaussian closure in CLUBB are the most influential parameters on low-cloud feedbacks. Our results suggest that a unified treatment of shallow convection and turbulence may give rise to the predominate role of the PBL turbulent mixing in determining low-cloud feedback.},
doi = {10.1029/2018MS001423},
journal = {Journal of Advances in Modeling Earth Systems},
issn = {1942-2466},
number = 11,
volume = 10,
place = {United States},
year = {2018},
month = {11}
}