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Published April 27, 2016 | Published + Supplemental Material
Journal Article Open

Meteorological and aerosol effects on marine cloud microphysical properties


Meteorology and microphysics affect cloud formation, cloud droplet distributions, and shortwave reflectance. The Eastern Pacific Emitted Aerosol Cloud Experiment and the Stratocumulus Observations of Los-Angeles Emissions Derived Aerosol-Droplets studies provided measurements in six case studies of cloud thermodynamic properties, initial particle number distribution and composition, and cloud drop distribution. In this study, we use simulations from a chemical and microphysical aerosol-cloud parcel (ACP) model with explicit kinetic drop activation to reproduce observed cloud droplet distributions of the case studies. Four cases had subadiabatic lapse rates, resulting in fewer activated droplets, lower liquid water content, and higher cloud base height than an adiabatic lapse rate. A weighted ensemble of simulations that reflect measured variation in updraft velocity and cloud base height was used to reproduce observed droplet distributions. Simulations show that organic hygroscopicity in internally mixed cases causes small effects on cloud reflectivity (CR) (<0.01), except for cargo ship and smoke plumes, which increased CR by 0.02 and 0.07, respectively, owing to their high organic mass fraction. Organic hygroscopicity had larger effects on droplet concentrations for cases with higher aerosol concentrations near the critical diameter (namely, polluted cases with a modal peak near 0.1 µm). Differences in simulated droplet spectral widths (k) caused larger differences in CR than organic hygroscopicity in cases with organic mass fractions of 60% or less for the cases shown. Finally, simulations from a numerical parameterization of cloud droplet activation suitable for general circulation models compared well with the ACP model, except under high organic mass fraction.

Additional Information

© 2016 American Geophysical Union. Received 13 DEC 2015; Accepted 21 MAR 2016; Accepted article online 29 MAR 2016; Published online 25 APR 2016. This work was funded by NSF AGS-1013423, NSF AGS-1360645, NSF AGS-1008848, DOE DE-SC0006679, ONR grants N00014-11-1-0783, N00014-10-1-0200, and N00014-10-1-0811, and EC Finance ID 1300359. Kevin J. Sanchez appreciates the support of the San Diego Foundation. We gratefully acknowledge the help and support of the crew and staff of the R/V Point Sur and the CIRPAS Twin Otter, as well as assistance from Bill Shull and Ken Duff of Scripps Institution of Oceanography. Finally, we thank Bruce Albrecht for the ceilometer measurements taken on both the SOLEDAD and E-PEACE campaigns. Corresponding data can be found at http://aerosols.ucsd.edu/SANCHEZetal2016_data.html.

Attached Files

Published - Sanchez_et_al-2016-Journal_of_Geophysical_Research__Atmospheres.pdf

Supplemental Material - jgrd52870-sup-0001-SI.docx


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