Turbidity

The potential global radiation is multiplied by a turbidity function to calculate the global radiation (c.f. eq. (4.89)). There are two optional ways of calculating turbidity (see switch Turbidity).

Turbidity can either be a function of the relative duration of sunshine, n_sun, (i.e. 1-n_c), and the global radiation is thus calculated with Ångström’s formula as:

                                                  (4.102)

where r₅ and r₆ are turbidity constants. See viewing function Ångströms Short wave equation.

As an alternative to Eq. (4.102) (only if within day resolution is chosen) the global radiation can be calculated with a flexible atmospheric turbidity, which is calculated as a function of solar inclination, humidity and cloudiness:

         (4.103)

 

where τ_Raileigh, τ_gas, τ_vapour and τ_aerosol, are functions describing the transmittance of solar radiation due to:

(1) Raileigh scattering:

                                      (4.104)

(2) Ozone:

      (4.105)

 

 

(3) Mixed gases:

                                                      (4.106)

(4) Water vapour:

     (4.107)

 

(5) Aerosols:

                                      (4.108)

Unexplained symbols in equation (4.104)-(4.108) are either functions or constants summarized in the table below:

Functions	Meaning
	optical parameter
	optical parameter
	used in water vapour function
	used in aerosol function
	used in ozone function
	Air pressure at the elevation of the simulated profile
Constants	Meaning
	ozone layer thickness (cm)
,	Angström coefficients
	Air pressure (hPa)

T_airK is air temperature in degrees Kelvin and D_elev (i.e. e_levsim - e_levmet) is the elevation difference between the meteorological station and the simulated profile.