Entrainment Processes at the Top of the Stable Marine Atmospheric Boundary Layer

University Of California-San Diego Scripps Inst Of Oceanography, La Jolla CA

Investigators

Abstract

This project, conducted with the collaboration of co-investigator Ian M. Brooks, is motivated by the need for a better understanding of mixing processes at the top of the marine boundary layer. During the summer months, the West Coast of the United States is a region of widespread and persistent stratocumulus clouds. The distribution of the clouds is highly variable and difficult to forecast accurately because of the extreme sensitivity of the predicted cloudiness to changes in the boundary conditions at cloud top. The clouds are limited in vertical development by a temperature inversion. Whether they persist or dissipate is determined in part by the rate of entrainment of dry air from above the inversion into the cloudy air. The purpose of the project is to investigate the mixing process using existing remote-sensing and in-situ data. In the summer of 1996, the C-130 research aircraft operated by the National Center for Atmospheric Research flew a series of eleven research flights off the coast of northern California and Oregon. Measurements included high-resolution, downward-pointing lidar observations of the boundary layer structure and aircraft traverses through the boundary layer, measuring the atmospheric stability, wind, and turbulence. This study goes beyond the original intention of the experiment by focusing on the effects of wind shear at the inversion level on the turbulence and mixing processes. The result will improve insight on the relative importance of shear and stability on entrainment.