Meteorological and aerosol effects on marine cloud microphysical properties

TitleMeteorological and aerosol effects on marine cloud microphysical properties
Publication TypeJournal Article
Year of Publication2016
AuthorsSanchez K.J, Russell LM, Modini RL, Frossard AA, Ahlm L, Corrigan CE, Roberts GC, Hawkins L.N, Schroder JC, Bertram A.K, Zhao R., Lee A.KY, Lin JJ, Nenes A, Wang Z, Wonaschutz A, Sorooshian A, Noone K.J, Jonsson H, Toom D., Macdonald A.M, Leaitch WR, Seinfeld JH
JournalJournal of Geophysical Research-Atmospheres
Date Published2016/04
Type of ArticleArticle
ISBN Number2169-897X
Accession NumberWOS:000378318100025
Keywords2011 e-peace; chemical-composition; climate models; condensation nucleus activity; counterflow virtual impactor; droplet formation; global; hygroscopic growth; mixed-phase clouds; organic aerosol; stratocumulus clouds

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 mu m). 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.

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