Case Studies of the Structure of the Atmospheric Boundary Layer Entrainment Zone.
AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH
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The structure of the atmospheric entrainment zone, an interfacial layer betweeen the convective boundary layer and the stable air aloft, is studied using data obtained during Boundary Layer Experiment 1983 in Oklahoma. Coincident high resolution aircraft and lidar observations provided a unique picture of the daytime continental entrainment zone. Fast-response Lyman alpha hygrometer output voltages from the aircraft are calibrated to yield meteorological units of humidity. Humidity values indicative of surface layer air are observed at all levels within rising thermals, and the corresponding top-hat humidity cross sections suggest little lateral entrainment. Two approaches are taken to describe the humidity structure of the entrainment zone. The first uses the linear mixing character of specific humidity. This yields vertical profiles of the proportion of surface layer air that are described well by the cumulative distribution function of asymmetrical double exponential functions. The second approach models frequency distributions of three types of air in the entrainment zone unmixed free atmosphere dry unmixed surface layer air moist and a mixture of these two. These results can be useful in cloud models and for future studies of the boundary layer.