A STUDY OF THE TRANSITIONAL BOUNDARY LAYER AND TURBULENCE DECAY
W. J. Shaw Pacific Northwest National Laboratory
ABSTRACT
We propose to carry out a study of the evolution of the turbulence structure of the atmospheric boundary layer, with an emphasis on the nature of the decay of turbulence during the transition period from day to night. The objectives of the study are: to develop from observations a general description of the evolution of atmospheric boundary layer turbulence during non-stationary periods, particularly the transition from day to night, in an urban valley; to evaluate the applicability of recently proposed velocity and time scales for decaying turbulence to practical boundary layer measurements; and to determine, from measurements and simulations, whether modifications of conventional subgrid-scale representations of turbulence in numerical models may be required to properly represent vertical mixing in non-stationary conditions. The measurements are described in the context of an anticipated month-long field campaign in the Salt Lake Valley in Utah. The project will use at least one wind profiler/RASS and a minisodar to obtain profiles of atmospheric boundary layer mean and turbulence variables continuously for the duration of the field campaign. The study will incorporate and automate recent developments in the processing of wind profiler data to increase the frequency and accuracy of the wind profiler/RASS data. The observational work will also make use of tower-mounted sonic anemometers to provide a measure of changing surface turbulence fluxes. The analysis will include a comparison of observations with direct numerical simulation (DNS) of the decaying turbulence field driven by the measured surface heat flux.
