Large-Scale Eddies in the Unstably Stratified Atmospheric Surface Layer. Part II: Turbulent Pressure Fluctuations and the Budgets of Heat Flux, Stress and Turbulent Kinetic Energy

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  • 1 Department of Atmospheric Sciences, University of Washington, Seattle, WA 98195
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Abstract

A method is developed for retrieving turbulent pressure fluctuations from tower measurements of velocity and temperature, through use of the equations of motion. This method is applied to a series of large-scale eddies which are defined by their characteristic temperature ramp structure. The variance of pressure is found to follow local free-convection.

Large-scale eddy (LSE) pressure fields are used to estimate the pressure transport and pressure-gradient interaction terms in the convective surface-layer budgets of heat flux, stress and turbulent kinetic energy. The LSE pressure terms are found to balance the budgets to within 20–30% of the size of the largest budget terms.

Ensemble fields are formed by averaging individual LSE pressure transport and pressure-gradient interaction fields. The basic characteristics of these ensemble pressure covariance fields are easily related to the cross-products of the ensemble fields of p′, ∂p′/∂x, w′, and so on. This offers a simple way of visualizing the source of the budget pressure covariances in terms of the average LSE structure.

Abstract

A method is developed for retrieving turbulent pressure fluctuations from tower measurements of velocity and temperature, through use of the equations of motion. This method is applied to a series of large-scale eddies which are defined by their characteristic temperature ramp structure. The variance of pressure is found to follow local free-convection.

Large-scale eddy (LSE) pressure fields are used to estimate the pressure transport and pressure-gradient interaction terms in the convective surface-layer budgets of heat flux, stress and turbulent kinetic energy. The LSE pressure terms are found to balance the budgets to within 20–30% of the size of the largest budget terms.

Ensemble fields are formed by averaging individual LSE pressure transport and pressure-gradient interaction fields. The basic characteristics of these ensemble pressure covariance fields are easily related to the cross-products of the ensemble fields of p′, ∂p′/∂x, w′, and so on. This offers a simple way of visualizing the source of the budget pressure covariances in terms of the average LSE structure.

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