psyc_cons {MeTo}

psychrometric constant

Description

The psychrometric constant [kPa/degreeC]

Usage

psyc_cons(elev, P = NULL, control = list())

Arguments

elev

elevation [m]

P

atmospheric pressure [kPa]

control

list for control parameters and empirical factors defined in controlDefaults and constDefaults (see Details)

Details

control:

Tko: reference temperature [degreeC] at elevation z0. Only needed if atmospheric pressure is missing. Often assumed to be 20 degreeC

elev: station elevation above sea level [m]. Needed if P = NULL for estP

lambda: latent heat of vaporization [MJ/kg]

eps: ratio molecular weight of water vapor/dry air = 0.622

cp: specific heat of moist air = 1.013 x 10-3 [MJ/(kg degreeC)]

Value

psychrometric constant [kPa/degreeC]

Note

eq. 8 of reference

References

Allen, R. G., Pereira, L. S., Raes, D., & Smith, M. (1998). Crop evapotranspiration-Guidelines for computing crop water requirements-FAO Irrigation and drainage paper 56. FAO, Rome, 300(9).

Examples

psyc_cons(elev = 2, P = 101.3)