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Compensating Errors in Cloud Radiative and Physical Properties over the Southern Ocean in the CMIP6 Climate Models

Zhao, Lijun and Wang, Yuan and Zhao, Chuanfeng and Dong, Xiquan and Yung, Yuk L. (2022) Compensating Errors in Cloud Radiative and Physical Properties over the Southern Ocean in the CMIP6 Climate Models. Advances in Atmospheric Sciences, 39 . pp. 2156-2171. ISSN 0256-1530. doi:10.1007/s00376-022-2036-z.

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The Southern Ocean is covered by a large amount of clouds with high cloud albedo. However, as reported by previous climate model intercomparison projects, underestimated cloudiness and overestimated absorption of solar radiation (ASR) over the Southern Ocean lead to substantial biases in climate sensitivity. The present study revisits this long-standing issue and explores the uncertainty sources in the latest CMIP6 models. We employ 10-year satellite observations to evaluate cloud radiative effect (CRE) and cloud physical properties in five CMIP6 models that provide comprehensive output of cloud, radiation, and aerosol. The simulated longwave, shortwave, and net CRE at the top of atmosphere in CMIP6 are comparable with the CERES satellite observations. Total cloud fraction (CF) is also reasonably simulated in CMIP6, but the comparison of liquid cloud fraction (LCF) reveals marked biases in spatial pattern and seasonal variations. The discrepancies between the CMIP6 models and the MODIS satellite observations become even larger in other cloud macro- and micro-physical properties, including liquid water path (LWP), cloud optical depth (COD), and cloud effective radius, as well as aerosol optical depth (AOD). However, the large underestimation of both LWP and cloud effective radius (regional means ∼20% and 11%, respectively) results in relatively smaller bias in COD, and the impacts of the biases in COD and LCF also cancel out with each other, leaving CRE and ASR reasonably predicted in CMIP6. An error estimation framework is employed, and the different signs of the sensitivity errors and biases from CF and LWP corroborate the notions that there are compensating errors in the modeled shortwave CRE. Further correlation analyses of the geospatial patterns reveal that CF is the most relevant factor in determining CRE in observations, while the modeled CRE is too sensitive to LWP and COD. The relationships between cloud effective radius, LWP, and COD are also analyzed to explore the possible uncertainty sources in different models. Our study calls for more rigorous calibration of detailed cloud physical properties for future climate model development and climate projection.

Item Type:Article
Related URLs:
URLURL TypeDescription
Zhao, Lijun0000-0002-7140-8105
Wang, Yuan0000-0001-6657-8401
Zhao, Chuanfeng0000-0002-5196-3996
Dong, Xiquan0000-0002-3359-6117
Yung, Yuk L.0000-0002-4263-2562
Additional Information:Drs. Yuan WANG, Xiquan DONG, and Yuk YUNG are supported by the National Science Foundation grants (Grant Nos. AGS-1700727/1700728 and 2031751/2031750). Dr. Chuanfeng ZHAO is supported by the National Natural Science Foundation of China. (Grant No. 41925022).
Funding AgencyGrant Number
National Natural Science Foundation of China41925022
Record Number:CaltechAUTHORS:20220926-576500100.6
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:117139
Deposited By: Melissa Ray
Deposited On:03 Oct 2022 22:23
Last Modified:01 Nov 2022 22:55

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