Stratiform Cloud Formation in the Marine Boundary Layer

Abstract

Observations of stratiform clouds in a region several hundred kilometers west of the southern California coast were made from the NCAR Electra research aircraft in the summer of 1987 during the First ISCCP (International Satellite Cloud Climatology Project) Regional Experiment (FIRE). Examples are shown of how heating or cooling of air by the sea and the evaporation of precipitation affect the stability of the temperature profile above the surface layer, which in turn affects the vertical moisture transports and the resulting cloud formation. We expect that sea-surface heating leads to the formation of stratus layers, while sea-surface cooling or cooling from evaporation of precipitation may produce fields of cumuli. The observations lead to a conceptual model of the life cycle of a stratus layer, starting as a thin, rather homogeneous layer, which grows and becomes patchy with time, produces precipitation, followed by formation of small cumuli below, and finally disintegrates, leaving a field of cumuli behind.