Cloudiness and sunshine

Relative cloudiness, n_c , can be used to calculate relative duration of sunshine, n_sun:

                                                               (4.84)

Duration of bright sunshine, ∆t_sun, can also be used to estimate relative duration of sunshine:

                                                               (4.85)

 

Daylength in minutes, ∆t_max, is calculated as a function of the latitude, l_at and day of the year t_day:

                                   (4.86)

 

where rad is a conversion factor from degrees to radians (π/180) and the argument in the arc cosines function a₁ is given as:

                  (4.87)

 

where the declination D_ec is given as:

                                 (4.88)

 

where t_day is day number of the year.