# WEM | Water Engineering

Applied Ecohydrology

# Extraterrestrial solar radiation

The extraterrestrial solar radiation can be estimated from simple geometric relationships. The distance between the sun and the earth $d_{se}$ is needed. The formula for the extraterrestrial incoming radiation $S_{ext}$ reads:

$$S_{ex} = 15.392*d_{se} * (\omega_s * sin(\phi)*sin(\delta)+cos(\phi)*cos(\delta)*sin(\omega_s))$$

The result is in $mm/day$ of water that can be evaporated with the corresponding amount of energy. $\phi$ is the latitude.

from pylab import *
from numpy import *
ds=0.4093*sin(2*pi/365*J-1.405)      # to be replaced by class
sha=arccos(-tan(latitude)*tan(ds))   # to be replaced by class
dse=1+0.033*cos(2*pi/365*J)
Sext=15.392*dse*(sha*sin(latitude)*sin(ds)+cos(latitude)*cos(ds)*sin(sha))
return Sext
latitude=31
J=arange(1,365,1)
show()