Pockets of Open Cells (POCs) and Drizzle in Marine Stratocumulus

Bjorn Stevens , Gabor Vali, Kimberly Comstock, Robert Wood, Margreet C. van Zanten, Philip H. Austin, Christopher S. Bretherton, Donald H. Lenschow
Bull. Amer. Meteor. Soc., 86, 51-57

Abstract

Data from recent field studies in the northeast and southeast Pacific are used to investigate pockets of open cells (POCs) embedded in otherwise uniform stratocumulus. The cellular structure within a POC resembles broader regions of open cellular convection typically found futher offshore. In both regions, cells are comprised of precipitating cell walls and cell interiors with depleted cloud water, and even clearing. POCs are long lived and embedded in broader regions of stratocumulus where average droplet sizes are relatively large. In contrast, stratiform, or unbroken, cloud formations tend to be accompanied by less, or no, drizzle suggesting that precipitation is necessary for the sustenance of the open cellular structure. Because, by definition, open cells are associated with a reduction in cloud cover these observations provide direct evidence of a connection between cloudiness and precipitation -- a linchpin of hypotheses which posit a connection between changes in the atmospheric aerosol and climate.

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