Bowen Ratio

The comparison between the amount of sensible heat and the amount of latent heat is often important when determining energy balance. As a quick method to compare the amount of sensible heat energy to the amount of latent heat energy, the Bowen Ratio was developed. It has the following form:

where B0 is the Bowen Ratio value, HS is the sensible heat, and HL is the latent heat. In situations where there is little moisture available, the HL value will be small, and the Bowen Ratio will be greater than one. In situations where it is very humid, the HL value will be large, and the Bowen Ratio will be less than one. In situations where the amount of sensible heat energy is near the amount of latent heat energy, the Bowen Ratio will be approximately one.

During the night, there is no incoming solar radiation, so the amount of sensible heat energy becomes minimal or even negative (loss of heat energy) . In these situations, the Bowen Ratio will be very small or even negative, as latent heat is not as dependent on incoming solar radiation.

Measuring the heat flux and partitioning the values between sensible and latent heat components is not a simple exercise. Thus, lookup tables of B0 values are usually used, especially in newer air quality models, that are representative of different land uses, seasons, and "wet" or "dry" surface conditions.

Quick Quiz: Which would you expect to have a higher Bowen ratio?
A humid day
A humid night
An arrid day
An arrid night

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