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In the subtropics, large regions of stratocumulus (Sc) clouds lie trapped between warm subsiding air and the cool sea surface off the west coasts of continents. These Sc clouds are relatively warm, with tops less than 1–2 km, so they emit nearly as much longwave radiation as the sea surface beneath them. The Sc clouds are also typically optically thick, reflecting much of the incident solar radiation. Because of these characteristics and the vast areal extent of the Sc regions, these clouds have a significant cooling effect on the earth’s radiation budget. |
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The radiative properties of Sc are dependent on cloud thickness and cloud fraction. These, in turn, are regulated by small-scale turbulent fluxes and a complex set of interactions within the shallow marine boundary layer. Currently, most climate models poorly represent the Sc cloud properties relevant to albedo. Observations from the East Pacific Investigation of Climate Stratocumulus (EPIC Sc) 2001 field campaign were designed to explore the relationships among the diurnal cycle, mesoscale structure, and precipitation in the stratocumulus region in the southeast Pacific. |
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Observations obtained during EPIC Sc include meteorological time series and observations from a scanning C-band radar, vertically pointing cloud radar, and ceilometer, as well as satellite data. |
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Findings to date include that drizzle is associated with increased variability in cloud and boundary layer properties compared to nondrizzling periods and that coherent patches of drizzle, or “cells,” can have large areas with radar reflectivities of greater than 5 dBZ of up to about 100 km2. Individual cells have long lifetimes, up to 2 h, and appear to be replenished by moisture in the boundary layer. |
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Work has been done in collaboration with Kim Comstock, Rob Wood and Chris Bretherton of University of Washington. |
