This project is a study of the atmospheric boundary layer, that layer near the surface of the Earth where turbulent air motions transfer heat, moisture, and momentum between the atmosphere and the Earth. Most past studies have treated this layer as being in a steady state, but transitions occur continually and influence its structure. The boundary layer undergoes a diurnal cycle that moves from a stable nighttime layer through transitional states to a midday convective period and then again through transitional states back to stable nighttime condition. This study will focus on the transition periods and the mid-day convective period. The primary tool to be used is large-eddy simulation (LES), a model technique in which turbulent motions larger than some specified size are represented explicitly while the average influence of the motions at smaller sizes is represented in parameterized form. To complement the LES results, the investigators also will examine observations from a set of well-documented past experiments that have studied the boundary layer in different locations. The expected results will be an extension of knowledge of boundary layer structure to periods of transition and a better understanding of the ways in which transitory turbulence affects that layer.
A long-range benefit of this and similar studies will be better representation of the boundary layer in weather and climate models. Such models must represent realistic fluxes of heat, moisture, and momentum between the Earth and the atmosphere but cannot resolve the fine-scale structures responsible for such fluxes. As a result, the fluxes must be represented parameterically in terms of large-scale variables. The development of accurate parametric representations will rely on results from detailed studies like this one. The project will also benefit future work in this area of research by providing training for a graduate student.
