One goal of the East Pacific Investigation of Climate (EPIC) is a better observational description of the extensive stratocumulus cloud-topped boundary layer that overlies the subtropical and near-equatorial southeast Pacific Ocean. Despite being the world's most persistent subtropical stratocumulus regime, with strong feedbacks to ENSO, this region has seen almost no detailed in-situ observations of the cloud and PBL. Another scientific goal was to assess the role of precipitation processes (in comparison to radiatively-driven turbulent entrainment of overlying dry air) in regulating the cloud thickness in this region.

As part of EPIC, the Ron Brown, a NOAA research vessel, took a two week cruise in October 2001 from the Galapagos Islands (90 W 2S) in the equatorial cold tongue to the northern Chilean coast, mostly about 1000-1500 km offshore, with extensive instrumentation for boundary layer and cloud sensing. NOAA/ETL deployed a 3 mm vertically pointing 'cloud' radar, a lidar, a microwave radiometer, and surface turbulent and radiative flux instrumentation. The University of Washington operated a 5 cm scanning (precipitation) radar and launched three-hourly radiosondes. The University of Mexico undertook aerosol sampling.

We present scientific highlights from this cruise. The PBL was 1000-1200 m deep and almost fully covered with clouds up to 500 m deep. In the NE Pacific, PBLs of this depth are usually decoupled, with a cumulus layer rising into the main stratocumulus deck, but the SE Pacific PBL was almost exclusively fairly well-mixed, under a strong capping inversion of around 10 K. Radar-detectable drizzle was observed within 20 km of the ship most of the time, except in the polluted air near the Chilean coast. It was frequently organized in mesoscale cells. A surprisingly regular diurnal cycle with pronounced maxima of inversion height, cloud thickness, and drizzle in the early morning was observed. By the conference, we hope to enhance our portrait with quantitative estimates of entrainment rate, vertical water fluxes due to drizzle, and an analysis of relevant collocated satellite retrievals from TERRA (MODIS), TRMM(TMI) and GOES.