Cloud microphysical characteristics of the entrainment-mixing processes in the marine stratocumulus clouds observed during the VOCALS project

The entrainment-mixing processes in marine stratocumulus clouds are studied by using the observational data from the G-1 aircraft during the VOCALS [VAMOS (Variability of the American Monsoon Systems) Ocean-Cloud-Atmosphere-Land Study] project, which was held in October-November 2008. The G-1 aircraft measured cloud microphysical and thermodynamic parameters from the persistent marine stratocumulus decks that form over the Southeast Pacific region off the coast of Chile and Peru. Entrainment zones in observed marine stratocumuli were generally classified into three mixing states, “inhomogeneous mixing”, “no mixing” and “post inhomogeneous mixing”, by using four different mixing diagrams. The relationships among the parameters, cloud droplet concentrations, liquid water contents, mean volume radius and liquid water potential temperatures, are shown up differently in the mixing diagrams depending on the mixing states. Cases classified as inhomogeneous mixing show relationships that were close to what was expected from inhomogeneous mixing and no mixing cases do not show any consistent relationships. Post inhomogeneous mixing cases showed microphysical characteristics roughly similar to inhomogeneous mixing and a hypothesis was suggested to explain these results. There are no cases that showed cloud microphysical relationships that were expected from homogeneous mixing in the G-1 aircraft measurement data during the VOCALS project. These results were consistent with the fact that the estimated time scale for complete droplet evaporation (τ_d) was much shorter than the estimated time scale for complete homogenization by turbulent diffusion (τ_T). More detail will be presented at the conference.