The purpose of this project is to improve our understanding of the exchange of heat, moisture, momentum, and contaminants between the earth's surface and the lower atmosphere when the atmospheric layer near the ground is extremely stable. In these conditions, the variation of the wind with height and time and the vertical transport of heat and other material by the atmosphere do not conform to the theories appropriate for daytime conditions. During the day surface heating causes the air next to the ground to become unstable, leading to convection, well developed turbulence, predictable profiles of temperature, wind velocity, and humidity, and therefore predictable vertical fluxes of heat and water vapor. But at night the surface is cold, the air stable, and the turbulence often intermittent and caused by vertical wind shear associated with terrain-induced drainage flows. The approach is to analyze existing data from twelve different field programs, which represent different kinds of terrain and climatic conditions, to determine new ways to express the fluxes in terms of wind speed, surface temperature, and other known quantities. The study will compare the observations with existing theories, seek ways of improving the theories, and assess the importance of turbulence induced by elevated shear layers in transporting material down to the ground. The result of the research will be an improved formulation of the very stable boundary layer for use in large scale
