Surface-based observations of mesoscale cumulus-stratocumulus interaction during ASTEX

Data obtained from the island of Santa Maria in the Azores, during the Atlantic Stratocumulus Transition Experiment (ASTEX) are used to describe cloud and boundary-layer structure for a 24-h period on 15 June 1992 over the east-central Atlantic (37°N, 25°10′W). The evolution of the mesoscale cloud structure during a 24-h period in the vertical column above the surface site was characterized using a 94-GHz radar, a laser ceilometer, 3-h radiosonde ascents, and surface micrometeorological instrumentation. Mesoscale circulations and drizzle were found to be key elements of the boundary-layer clouds observed in this region. It was suggested that the enhanced precipitation due to cumulus convection may be an important feedback mechanism between the cloud and subcloud layers in the transition region. -from Authors