Preprints
https://doi.org/10.5194/egusphere-2023-2161
https://doi.org/10.5194/egusphere-2023-2161
06 Nov 2023
 | 06 Nov 2023

Droplet collection efficiencies estimated from satellite retrievals constrain effective radiative forcing of aerosol-cloud interactions

Charlotte M. Beall, Po-Lun Ma, Matthew W. Christensen, Johannes Mülmenstädt, Adam Varble, Kentaroh Suzuki, and Takuro Michibata

Abstract. Process-oriented observational constraints for the anthropogenic effective radiative forcing due to aerosol-cloud-interactions (ERFaci) are highly desirable because the large uncertainty associated with ERFaci poses a significant challenge to climate prediction. The satellite-based Contoured Frequency by Optical Depth Diagrams (CFODD) analysis was previously proposed to support evaluation of model representation of cloud liquid to rain conversion processes because the slope of a CFODD, generated from joint MODerate Resolution Imaging Spectroradiometer (MODIS)-CloudSat cloud retrievals, provides an estimate of cloud droplet collection efficiency in single-layer warm liquid clouds (SLWCs). Here we present an updated CFODD analysis as an observational constraint for the ERFaci due to warm rain processes and apply it to the U.S. Department of Energy’s Energy Exascale Earth System Model version 2 (E3SMv2). Updates to the CFODD analysis include multiple changes to the SLWC detection algorithm for better consistency between MODIS-CloudSat observations and the satellite simulators, as well as the estimation of CFODD slopes using Random Sample Consensus robust linear regression. A series of sensitivity experiments shows that E3SMv2 droplet collection efficiencies and ERFaci are highly sensitive to the treatment of autoconversion, the rate of mass transfer from cloud liquid to rain, yielding a strong correlation between the CFODD slope and the shortwave component of ERFaci (Pearson’s R = -0.91). We estimate the shortwave component of ERFaci (ERFaciSW), constrained by MODIS-CloudSat, by calculating the intercept of the linear association between E3SMv2 ERFaciSW and the CFODD slopes, using the MODIS-CloudSat CFODD slope as a reference. When E3SMv2’s droplet collection efficiency is constrained to agree with the A-Train retrievals, ERFaciSW is reduced by 13 % in magnitude, indicating that correcting bias in the ERFaciSW due to autoconversion would bring E3SMv2’s total ERFaci (-1.50 W m-2) into better agreement with the IPCC AR6 ‘very likely’ range for ERFaci (-1.0 ± 0.7 W m-2). This study provides a new process-oriented observational constraint for ERFaci due to warm rain processes to reduce the uncertainty of climate predictions.

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Journal article(s) based on this preprint

07 May 2024
Droplet collection efficiencies inferred from satellite retrievals constrain effective radiative forcing of aerosol–cloud interactions
Charlotte M. Beall, Po-Lun Ma, Matthew W. Christensen, Johannes Mülmenstädt, Adam Varble, Kentaroh Suzuki, and Takuro Michibata
Atmos. Chem. Phys., 24, 5287–5302, https://doi.org/10.5194/acp-24-5287-2024,https://doi.org/10.5194/acp-24-5287-2024, 2024
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.

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Single-layer warm liquid clouds cover nearly one-third of the earth's surface, and uncertainties...
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