Mesoscale Variability and Drizzle in Southeast Pacific Stratocumulus

Abstract

Observations from the East Pacific Investigation of Climate (EPIC) 2001 field campaign are well suited for exploring the relationships among the diurnal cycle, mesoscale (10?100 km) structure, and precipitation in the stratocumulus region in the southeast Pacific. Meteorological time series and observations from a scanning C-band radar, vertically pointing cloud radar, and ceilometer, as well as satellite data, are used to show that drizzle is associated with increased variability in cloud and boundary layer properties compared to nondrizzling periods. The stratocumulus-topped boundary layer is typically well mixed at night, transitioning to less well mixed in the afternoon, with drizzle most frequently occurring in the early morning. 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.