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Thermodynamic and Aerosol Controls in Southeast Pacific Stratocumulus

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https://ir.library.oregonstate.edu/concern/articles/v979v4491

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  • A near-large-eddy simulation approach with size-revolving (bin) microphysics is employed to evaluate the relative sensitivity of southeast Pacific marine boundary layer cloud properties to thermodynamic and aerosol parameters. Simulations are based on a heavily drizzling cloud system observed by the NOAA ship Ronald H. Brown during the Variability of the American Monsoon Systems (VAMOS) Ocean Cloud Atmosphere Land Study Regional Experiment (VOCALS-Rex) field campaign. A suite of numerical experiments examines the sensitivity of drizzle to variations in boundary layer depth and cloud condensation nuclei (CCN) concentration in a manner consistent with the variability of those parameters observed during VOCALS-Rex. All four simulations produce cellular structures and turbulence characteristics of a circulation driven predominantly in a bottom-up fashion. The cloud and subcloud layers are coupled by strong convective updrafts that provide moisture to the cloud layer. Distributions of reflectivity calculated from model droplet spectra agree well with reflectivity distributions from the 5-cm-wavelength scanning radar aboard the ship, and the statistical behavior of cells over the course of the simulation is similar to that documented in previous studies of southeast Pacific stratocumulus. The simulations suggest that increased aerosol concentration delays the onset of drizzle, whereas changes in the boundary layer height are more important in modulating drizzle intensity.
  • Keywords: Part II, Numerical simulations, Diurnal cycle, Cloud condensation nuclei, Mesoscale cellular structures, Large eddy simulation, Shallow cumulus convection, Marine boundary layer, Explicit microphysics, Open cells
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  • Mechem, D., Yuter, S., & de Szoeke, S. (2012). Thermodynamic and aerosol controls in southeast pacific stratocumulus. Journal of the Atmospheric Sciences, 69(4), 1250-1266. doi: 10.1175/JAS-D-11-0165.1
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  • 69
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  • 4
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  • This investigation was supported by the University of Kansas General Research Fund allocation 230211 and New Faculty Startup funds, and U.S. National Oceanic and Atmospheric Administration (NOAA) Climate Program Office (CPO) Climate Prediction Program for the Americas (CPPA) Grants GC09-252b, GC09-507, and NA10OAR4310160.
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