Journal of Fluid Mechanics



Flux Richardson number measurements in stable atmospheric shear flows


E. R. PARDYJAK a1, P. MONTI a2 and H. J. S. FERNANDO a2
a1 Department of Mechanical Engineering, University of Utah, Salt Lake City, UT 84112, USA
a2 Environmental Fluid Dynamics Program, Department of Mechanical and Aerospace Engineering, Arizona State University, Tempe, AZ 85287-9809, USA

Abstract

The flux Richardson number Rf (also known as the mixing efficiency) for the stably stratified atmospheric boundary layer is investigated as a function of the gradient Richardson number Rig using data taken during two field studies: the Vertical Transport and Mixing Experiment (VTMX) in Salt Lake City, Utah (October 2000), and a long-term rural field data set from Technical Area 6 (TA-6) at Los Alamos National Laboratory, New Mexico. The results show the existence of a maximum Rf (0.4–0.5) at a gradient Richardson number of approximately unity. These large-Reynolds-number results agree well with recent laboratory stratified shear layer measurements, but are at odds with some commonly used Rf parameterizations, particularly under high-Rig conditions. The observed variations in buoyancy flux and turbulent kinetic energy production are consistent with the concept of global intermittency of the atmospheric stable boundary layer.

(Received September 28 2001)
(Revised February 20 2002)



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