The California Low-Level Coastal Jet and Nearshore Stratocumulus

Abstract

This observational study focus on the interaction between the coastal wind field and the evolution of the coastal stratocumulus clouds. The data were collected during an experiment in the summer of 1999 near the California coast with the Twin Otter research aircraft operated by the Center for Interdisciplinary Remote Piloted Aircraft Study (CIRPAS) at the Naval Postgraduate School (NPS). The wind components were measured with a DGPS/radome system, which provides a very accurate (0.1 ms-1) estimate of the wind (Kalogiros and Wang 2001). The instrumentation of the aircraft included fast sensors for the measurement of air temperature, humidity, shortwave and longwave radiation, sea surface temperature, liquid water and concentration and size of water droplets and aerosols. The synoptic conditions during the experimental period were typical of a high pressure system over the central Pacific Ocean with lower pressure over land and northerly winds in the 2km layer close to the surface. The wind speed was observed to increase in the boundary layer and a wind jet close to the boundary layer top was frequently observed some tens of kilometers offshore. In some occasions the wind jet was quite intense and affected significantly the structure of the stratocumulus layer.