A Modeling Study on the Fair Weather Marine Boundary Layer of the GATE

Abstract

A three-dimensional ensemble-mean atmospheric model, with simplified second-moment turbulence closure equations and a statistical treatment for the condensation process, is used to simulate a fair weather marine boundary layer observed during the GATE [GARP (Global Research Program) Atlantic Tropical Experiment]. The data deduced from airborne and surface-based instrumentation provided not only comprehensive initial and boundary conditions for the model but also permitted detailed comparisons between modeled and observed turbulence quantities. The modeled mean variables and turbulence quantities are found to agree well with observations and the results obtained by a large-eddy simulation. The cloud properties are also well reproduced in terms of the amount of cloud liquid water and fraction of cloud coverage. Other significant modeled features include high correlations between cloud liquid water and turbulence quantities; the entrainment process associated with negative virtual temperature flux near the top of the mixed-layer, and the well-balanced turbulence kinetic energy budget.