THE ATLANTIC STRATOCUMULUS TRANSITION EXPERIMENT - ASTEX

The Atlantic Stratocumulus Experiment (ASTEX) was conducted over the n ortheast Atlantic Ocean during June 1992 with substantial internationa l collaboration. The main goal of ASTEX was to study the climatologica lly important transition between solid stratocumulus and subtropical t rade cumulus cloud regimes using island, aircraft, ship, and satellite measurements. Typically, the boundary layer was found to support cumu lus clouds detraining into a patchy and fairly thin upper-stratocumulu s layer. The substantial microphysical variability between clean marin e and polluted continental air masses observed during ASTEX affected b oth drizzle and cloud properties. Highlights of the ASTEX research str ategy included use of the ECMWF operational forecast model for assimil ation of ASTEX soundings to obtain improved regional meteorological an alyses; ''Lagrangian'' measurements of boundary-layer evolution follow ing an air mass using aircraft and balloons, extensive coordinated use of surface, airborne, and satellite platforms; and an extensive suite of island-based remote sensing systems including millimeter-wavelengt h radars. A summary of ASTEX is presented and some initial results are presented.