Experimental Studies of Turbulence in the Surface Layer: Phase II

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The object of this research is a systematic evaluation of sources and sinks of turbulent kinetic energy in the atmospheric surface layer. Effects of stability on the normalized terms of the turbulent energy equation (the so-called "phi functions") are being investigated in a graduated series of comparatively small field experiments. The particular forms of and the empirical constants in relations for these functions now commonly used to parameterize the lower boundary layer remain uncertain because of contradictory results of subsequent experiments and incomplete investigation of the effects of stability. This experiment will measure wind profiles, turbulence spectra, surface thermal energy balances, and Bowen ratios in order to evaluate the effects of moderate departures from neutrality upon (1) the rates at which turbulence is produced by wind shear and buoyancy, (2) the turbulence dissipation rate, (3) the net rate at which energy is locally gained or lost by the sum of the divergence terms. To obtain this budget data, additional measurements will be added: the depth of the mixed layer will be monitored acoustically and the vertical turbulent flux of turbulent energy will be measured by two levels by eddy correlation. All field experiments will be conducted over extensive cropped surfaces of uniform roughness. Professor Frenzen is well qualified to make these measurements; he has considerable experience in previous field measurements especially in the use of his unique low-inertia anemometers.