The extraterrestrial solar radiation can be estimated from simple geometric relationships. The distance between the sun and the earth is needed. The formula for the extraterrestrial incoming radiation
reads:
The result is in of water that can be evaporated with the corresponding amount of energy.
is the latitude.
from pylab import * from numpy import * def extraterrestrialradiation(latitude,J): 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) plot(J,extraterrestrialradiation(latitude,J)) ytext = ylabel('extraterrestrial radiation in mm/day') xtext = xlabel('Julian day') show()