Development of a physically exact energy balance method for estimating evaporation from free water surfaces

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Title: Development of a physically exact energy balance method for estimating evaporation from free water surfaces
Author: Sharif, Muhammad
Abstract: Based upon hydrodynamic , thermodynamic , and meteorologic principles , a formula is proposed for estimating free water surface evaporation . The proposed formula considers the density and isobaric specific heat of the moist air as a variable depending on the amount of water vapor content in the constant flux boundary layer of the atmosphere . It has been shown that if the influence of the variation of atmospheric water vapor content through density and specific heat of the air is not considered , then the sensible heat flux as computed by conventional methods in the energy -based evaporation equations will be smaller by approximately 17 per cent in comparison to the latent heat flux . Consequently , this underestimation of sensible heat flux (as calculated conventionally ) results in a corresponding overestimate of the estimated evaporation . The eddy exchange coefficients for momentum , heat , and moisture have been incorporated in the prediction formula in the familiar form of turbulent Prandtl , turbulent Schmidt , and turbulent Lewis numbers . Thus the proposed prediction equation does not contain the often questioned assumption of the equality of these eddy transfer coefficients in evaporation equations . Evaporation data collected over water and well -watered short grass were used for checking the validity of the proposed prediction equation . These data were gathered under different conditions of the atmospheric stability , and under a wide range of wind velocities . The analysis of the data showed an excellent agreement between the predicted amounts of evaporation and the observations .
URI: http : / /hdl .handle .net /2346 /10387
Date: 1989-12

Citation

Sharif, Muhammad Development of a physically exact energy balance method for estimating evaporation from free water surfaces. Doctoral dissertation, Texas Tech University. Available electronically from http : / /hdl .handle .net /2346 /10387 .

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