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Bowen ratio

A Bowen ratio is the ratio of energy fluxes from one medium to another by sensible and latent heating respectively. It is calculated by the equation

$B = {\frac{Q_h}{Q_e}}$ ,

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where $Q h$ is sensible heating and $Q e$ is latent heating. The quantity was named by Harald Sverdrup after Ira Sprague Bowen (1898–1973), an astrophysicist whose theoretical work on evaporation to air from water bodies made first use of it, and it is used most commonly in meteorology and hydrology. In this context, when the magnitude of $B$ is less than one, a greater proportion of the available energy at the surface is passed to the atmosphere as latent heat than as sensible heat, and the converse is true for values of $B$ greater than one. As ${Q_e \rightarrow 0}$ , however, $B$ becomes unbounded making the Bowen ratio a poor choice of variable for use in formulae, especially for arid surfaces. For this reason the evaporative fraction is sometimes a more appropriate choice of variable representing the relative contributions of the turbulent energy fluxes to the surface energy budget.

The Bowen ratio is related to the evaporative fraction, $E F$ , through the equation,

${EF = \frac{Q_e}{Q_e + Q_h} = \frac{1}{1+B}}$ .

References

Bowen, I.S., 1926: The ratio of heat losses by conduction and by evaporation from any water surface. Physics Review, 27, pp 779—787.
Lewis, J.M., 1995: The Story behind the Bowen Ratio. Bulletin of the American Meteorological Society, 76, pp 2433-2443. [1]

Categories: Thermodynamics | Atmospheric thermodynamics