Penman equation
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The Penman equation describes evaporation (E) from an open water surface. It is widely regarded as one of the most accurate models, in terms of estimates.[citation needed] It was developed by Howard Penman at the Rothamsted Experimental Station, Harpenden, UK.
There are numerous versions of the Penman equation, one of which is:
where:
- m = Slope of the saturation vapor pressure curve (Pa K-1)
- Rn = Net irradiance (W m-2)
- ρa = density of air (kg m-3)
- cp = heat capacity of air (J kg-1)
- Cat = atmospheric conductance (m s-1)
- δe = vapor pressure deficit (Pa)
- λv = latent heat of vaporization (J kg-1)
- γ = psychrometric constant (Pa K-1)
which (if the SI units in parentheses are used) will give the evaporation E in units of kg/(m²·s), kilograms of water evaporated every second for each square meter of area.
[edit] Literature
Penman, H.L. (1948): Natural evaporation from open water, bare soil and grass. Proc. Roy. Soc. London A(194), S. 120-145.
