Solar_radiation

4461 days ago by comphy

Different calculations of solar noon

References:
[1] D. G. G. de Pury and G. D. Farquhar. Simple scaling of photosynthesis from leaves to canopies without the errors of big-leaf models. Plant Cell and Environment, 20(5):537–557, 1997.

[2] http://www.powerfromthesun.net/chapter3/Chapter3Word.htm#Equation%20of%20Time

 

 
var('td') le = 131 + 9.003/60 # longitude of Howards Springs site ls = 142.5 # standard longitude of time zone # Equations in dePury & Farquhar 1997 [1] Gd = 2/365*pi*(td - 1) # day angle (A18) eqt = 0.017 + 0.4281*cos(Gd) - 7.351*sin(Gd) - 3.349*cos(2*Gd) - 9.731*sin(Gd) # (A17) to = 12 + (4*(ls - le) - eqt)/60 # solar noon (A16) P = plot(to, (td,0,365), color = 'red') #Equations in [2] x = 360*(td - 1)/365.242*pi/180 # 3.3 eot = 0.258*cos(x) - 7.416*sin(x) - 3.648*cos(2*x) - 9.228*sin(2*x) # (3.2) lc = -(le - ls)/16 # longitude correction (3.6, changed sign for east of Greenwich) lct = 12 - eot/60 + lc # 3.5 P += plot(lct, (td,0,365), color = 'blue') P.axes_labels(['Day of year','Time of solar noon (hrs)']) P 
        

                                
                            

                            
                                

                                    

                                

                            
                                

                                    
                                

                        

                    		
                

            

        

        


    




  
    

    
    

      
Why are these different? According to Tom van Niel, the red curve may be neglecting the tilt of the Earth's axis. This is strange, 
as dePury & Farquhar 1997 took the equation from Iqbal 1983, which was 
obviously published after Woolf, 1968.