Physical processes in coastal stratocumulus clouds from aircraft measurements during UPPEF 2012

Abstract

The objective of this thesis was to perform the initial analysis of aircraft measurements from the field campaign of the Unified Physical Parameterization for Extended Forecast (UPPEF 2012). We examined the general characteristics of the observed stratocumulus-topped boundary layers and identified cases for future in-depth studies. We first determined the boundary layer heights from all sounding profiles. The results indicated the sharp westward increase of boundary layer height is limited to ~200 km offshore with an average slope of 2m per kilometer. Substantial west-east spatial variability of thermodynamic properties is also observed from vertical profiles. The sea surface temperature (SST) in the region varied significantly. Near surface measurements over the warm and cold SST regions for three cases were analyzed and compared. This research found that the small scale variability in the SST resulted in significant variation in the surface exchange of sensible and latent heat fluxes, and wind stress. Such variability makes it difficult to correctly parameterize surface fluxes. The presence of cool downdrafts in the upper cloud layer is evident in the joint probability density distribution and buoyancy flux profiles. The results from this research will guide future cloud parameterization scheme development in forecast models.