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Title: Cloud droplet size distribution broadening during diffusional growth: ripening amplified by deactivation and reactivation

Abstract

Cloud droplet size distributions (CDSDs), which are related to cloud albedo and lifetime, are usually broader in warm clouds than predicted from adiabatic parcel calculations. We investigate a mechanism for the CDSD broadening using a Lagrangian bin-microphysics cloud parcel model that considers the condensational growth of cloud droplets formed on polydisperse, sub-micrometer aerosols in an adiabatic cloud parcel that undergoes vertical oscillations, such as those due to cloud circulations or turbulence. Results show that the CDSD can be broadened during condensational growth as a result of Ostwald ripening amplified by droplet deactivation and reactivation, which is consistent with Korolev (1995). The relative roles of the solute effect, curvature effect, deactivation and reactivation on CDSD broadening are investigated. Deactivation of smaller cloud droplets, which is due to the combination of curvature and solute effects in the downdraft region, enhances the growth of larger cloud droplets and thus contributes particles to the larger size end of the CDSD. Droplet reactivation, which occurs in the updraft region, contributes particles to the smaller size end of the CDSD. In addition, we find that growth of the largest cloud droplets strongly depends on the residence time of cloud droplet in the cloud rather than themore » magnitude of local variability in the supersaturation fluctuation. This is because the environmental saturation ratio is strongly buffered by smaller cloud droplets. Two necessary conditions for this CDSD broadening, which generally occur in the atmosphere, are: (1) droplets form on polydisperse aerosols of varying hygroscopicity and (2) the cloud parcel experiences upwards and downwards motions. Therefore we expect that this mechanism for CDSD broadening is possible in real clouds. Our results also suggest it is important to consider both curvature and solute effects before and after cloud droplet activation in a cloud model. The importance of this mechanism compared with other mechanisms on cloud properties should be investigated through in-situ measurements and 3-D dynamic models.« less

Authors:
ORCiD logo [1];  [2]; ORCiD logo [3]; ORCiD logo [1]
  1. Brookhaven National Lab. (BNL), Upton, NY (United States)
  2. Brookhaven National Lab. (BNL), Upton, NY (United States); Stony Brook Univ., NY (United States)
  3. Michigan Technological Univ., Houghton, MI (United States)
Publication Date:
Research Org.:
Brookhaven National Lab. (BNL), Upton, NY (United States); Michigan Technological Univ., Houghton, MI (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
OSTI Identifier:
1438207
Report Number(s):
BNL-205676-2018-JAAM
Journal ID: ISSN 1680-7375
Grant/Contract Number:  
SC0012704; SC0011690
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Atmospheric Chemistry and Physics Discussions (Online)
Additional Journal Information:
Journal Name: Atmospheric Chemistry and Physics Discussions (Online); Journal ID: ISSN 1680-7375
Publisher:
European Geosciences Union
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES

Citation Formats

Yang, Fan, Kollias, Pavlos, Shaw, Raymond A., and Vogelmann, Andrew M.. Cloud droplet size distribution broadening during diffusional growth: ripening amplified by deactivation and reactivation. United States: N. p., 2017. Web. doi:10.5194/acp-2017-1125.
Yang, Fan, Kollias, Pavlos, Shaw, Raymond A., & Vogelmann, Andrew M.. Cloud droplet size distribution broadening during diffusional growth: ripening amplified by deactivation and reactivation. United States. doi:10.5194/acp-2017-1125.
Yang, Fan, Kollias, Pavlos, Shaw, Raymond A., and Vogelmann, Andrew M.. Wed . "Cloud droplet size distribution broadening during diffusional growth: ripening amplified by deactivation and reactivation". United States. doi:10.5194/acp-2017-1125. https://www.osti.gov/servlets/purl/1438207.
@article{osti_1438207,
title = {Cloud droplet size distribution broadening during diffusional growth: ripening amplified by deactivation and reactivation},
author = {Yang, Fan and Kollias, Pavlos and Shaw, Raymond A. and Vogelmann, Andrew M.},
abstractNote = {Cloud droplet size distributions (CDSDs), which are related to cloud albedo and lifetime, are usually broader in warm clouds than predicted from adiabatic parcel calculations. We investigate a mechanism for the CDSD broadening using a Lagrangian bin-microphysics cloud parcel model that considers the condensational growth of cloud droplets formed on polydisperse, sub-micrometer aerosols in an adiabatic cloud parcel that undergoes vertical oscillations, such as those due to cloud circulations or turbulence. Results show that the CDSD can be broadened during condensational growth as a result of Ostwald ripening amplified by droplet deactivation and reactivation, which is consistent with Korolev (1995). The relative roles of the solute effect, curvature effect, deactivation and reactivation on CDSD broadening are investigated. Deactivation of smaller cloud droplets, which is due to the combination of curvature and solute effects in the downdraft region, enhances the growth of larger cloud droplets and thus contributes particles to the larger size end of the CDSD. Droplet reactivation, which occurs in the updraft region, contributes particles to the smaller size end of the CDSD. In addition, we find that growth of the largest cloud droplets strongly depends on the residence time of cloud droplet in the cloud rather than the magnitude of local variability in the supersaturation fluctuation. This is because the environmental saturation ratio is strongly buffered by smaller cloud droplets. Two necessary conditions for this CDSD broadening, which generally occur in the atmosphere, are: (1) droplets form on polydisperse aerosols of varying hygroscopicity and (2) the cloud parcel experiences upwards and downwards motions. Therefore we expect that this mechanism for CDSD broadening is possible in real clouds. Our results also suggest it is important to consider both curvature and solute effects before and after cloud droplet activation in a cloud model. The importance of this mechanism compared with other mechanisms on cloud properties should be investigated through in-situ measurements and 3-D dynamic models.},
doi = {10.5194/acp-2017-1125},
journal = {Atmospheric Chemistry and Physics Discussions (Online)},
number = ,
volume = ,
place = {United States},
year = {Wed Dec 06 00:00:00 EST 2017},
month = {Wed Dec 06 00:00:00 EST 2017}
}

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