This function is used to estimate the The atmospheric pressure, P, by using a simplification of the ideal gas law, assuming 20<U+00B0>C for a standard atmosphere.
Please, see the equation 7 from the FAO Irrigation and drainage paper 56.
Usage
atm_pressure(z)
Arguments
z
Elevation above sea level in meters.
Value
Atmospheric pressure in kPa.
References
Allen et al., 1998. Crop Evapotranspiration. Guidelines for computing crop water requirements. FAO Irrigation and drainage paper 56.
http://www.fao.org/3/X0490E/x0490e00.htm.