Mixed-Layer Depth Model Based on Turbulent Energetics

Roland B. Stull Department of Atmospheric Sciences, University of Washington, Seattle 98195

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Abstract

Mixed layer depths are predicted using an entrainment equation with conservation equations. The entrainment equation is based on the turbulent kinetic energy equation for the mixed layer. The atmosphere is idealized as having temperatures, humidities and winds constant with height in the boundary layer with a step discontinuity marking the top of the mixed layer. This model is tested with mixed layer depth observations made during the 1953 Great Plains experiment, the 1967 Australian Wangara experiment, and the 1972 Puerto Rican tropical experiment. Model calculations of inversion rise and mixed layer depth offer good agreement with the observations. It is found that none of the turbulence generation and loss mechanisms for the mixed layer (such as buoyancy, wind shear and gravity waves) should be neglected a priori.

Abstract

Mixed layer depths are predicted using an entrainment equation with conservation equations. The entrainment equation is based on the turbulent kinetic energy equation for the mixed layer. The atmosphere is idealized as having temperatures, humidities and winds constant with height in the boundary layer with a step discontinuity marking the top of the mixed layer. This model is tested with mixed layer depth observations made during the 1953 Great Plains experiment, the 1967 Australian Wangara experiment, and the 1972 Puerto Rican tropical experiment. Model calculations of inversion rise and mixed layer depth offer good agreement with the observations. It is found that none of the turbulence generation and loss mechanisms for the mixed layer (such as buoyancy, wind shear and gravity waves) should be neglected a priori.

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