geocat.comp.crop.psychrometric_constant¶
- geocat.comp.crop.psychrometric_constant(pressure)¶
Compute psychrometric constant [kPa / C] as described in the Food and Agriculture Organization (FAO) Irrigation and Drainage Paper 56 entitled:
Crop evapotranspiration - Guidelines for computing crop water requirement. Specifically, see equation 7 of Chapter 3 or equation 3-2 in Annex 3.
From FAO 56:
The specific heat at constant pressure is the amount of energy required to increase the temperature of a unit mass of air by one degree at constant pressure. Its value depends on the composition of the air, i.e., on its humidity. For average atmospheric conditions a value cp = 1.013 10-3 MJ kg-1 C-1 can be used. As an average atmospheric pressure is used for each location (Equation 7), the psychrometric constant is kept constant for each location.
A table listing the psychrometric constant for different altitudes is located here: https://www.fao.org/3/X0490E/x0490e0j.htm
- Parameters
pressure (
numpy.ndarray
,xarray.DataArray
,list
,float
) – pressure in kPa/C- Returns
psy_const – the computed psychrometric constant. Same shape as pressure.
- Return type
Examples
>>> import numpy as np >>> from geocat.comp import psychrometric_constant >>> pressure = np.array([60, 80, 100]) >>> psychrometric_constant(pressure) array([0.0398844, 0.0531792, 0.066474 ])
See also
Related NCL Functions: psychro_fao56