The Bowen ratio is used to describe the type of

heat transfer Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy ( heat) between physical systems. Heat transfer is classified into various mechanisms, such as thermal conducti ...

for a surface that has moisture. Heat transfer can either occur as

sensible heat Sensible heat is heat exchanged by a body or thermodynamic system in which the exchange of heat changes the temperature of the body or system, and some macroscopic variables of the body or system, but leaves unchanged certain other macroscopic vari ...

(differences in temperature without

evapotranspiration Evapotranspiration (ET) is the combined processes by which water moves from the earth’s surface into the atmosphere. It covers both water evaporation (movement of water to the air directly from soil, canopies, and water bodies) and transp ...

) or

latent heat Latent heat (also known as latent energy or heat of transformation) is energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature process — usually a first-order phase transition. Latent heat can be underst ...

(the energy required during a change of state, without a change in temperature). The Bowen ratio is generally used to calculate heat lost (or gained) in a substance; it is the ratio of energy fluxes from one state to another by

and latent heating respectively. The ratio was named by Harald Sverdrup after

Ira Sprague Bowen Ira Sprague Bowen (December 21, 1898 – February 6, 1973) was an American physicist and astronomer. In 1927 he discovered that nebulium was not really a chemical element but instead doubly ionized oxygen. Life and work Bowen was born in Se ...

(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 Meteorology is a branch of the atmospheric sciences (which include atmospheric chemistry and physics) with a major focus on weather forecasting. The study of meteorology dates back millennia, though significant progress in meteorology did no ...

and

hydrology Hydrology () is the scientific study of the movement, distribution, and management of water on Earth and other planets, including the water cycle, water resources, and environmental watershed sustainability. A practitioner of hydrology is call ...

Formulation

The Bowen ratio is calculated by the equation: :

B =

, where

Q_h

is sensible heating and

Q_e

is latent heating. 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

, 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 The Bowen ratio is used to describe the type of heat transfer for a surface that has moisture. Heat transfer can either occur as sensible heat (differences in temperature without evapotranspiration) or latent heat (the energy required during a chan ...

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,

EF

, through the equation, :

. The Bowen ratio is an indicator of the type of surface. The Bowen ratio,

, is less than one over surfaces with abundant water supplies.

References

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External links

National Science Digital Library - Bowen Ratio
1926 introductions Engineering ratios Heat transfer Atmospheric thermodynamics {{meteorology-stub