global
Defined in ClassGlobal. This module calculates the theoretical interval short-wave direct and diffuse solar radiation. The routine handles GSL and ASL. There is an adjustment for elevation and transmissivity applicable to the region adjacent to the triangle, Edmonton, Winnipeg and Bad Lake. The interval and daily values are calculated by accumulating the 10 minute calculated values. The maximum number of daily sunshine hours is calculated. The theoretical direct-beam component of solar radiation is developed from an expression proposed by Garnier and Ohmura (1970). The solar angle is output for use in other modules. Extra variables have been added to help in determining if the module is malfunctioning
Observations
- none
Variables
- Qdro (W/m^2) - clear-sky direct.
- Qdfo (W/m^2) - clear-sky diffuse.
- Qdflat (W/m^2) - clear-sky direct + diffuse on a horizontal surface. Always independent of slope and aspect.
- QdflatE (W/m^2) - extraterrestrial radiation, i.e. no atmosheric attenuation. Always independent of slope and aspect.
- QdroD (MJ/m^2) - daily clear-sky direct.
- QdfoD (MJ/m^2) - daily clear-sky diffuse.
- QdflatD (MJ/m^2) - daily clear-sky direct on a horizontal surface. Now includes the diffuse.
- QdroDext (W/m^2) - daily extraterrestial direct. Always independent of slope and aspect.
- SolAng (r) - solar angle in radians.
- SunMax (h) - maximum sunshine hours.
- pQdro (MJ/m^2*int) - clear-sky direct.
- pQdfo (MJ/m^2*int) - clear-sky diffuse.
- pSol(r) - solar angle in radians.
Parameters
- hru_lat (°) - latitude. Positive value indicates northern hemisphere, negative value southern hemisphere.
- hru_elev (m) - altitude.
- hru_GSL (°) - ground slope - increasing the slope positively, tilts the plane to the north with ASL = 0.
- hru_ASL (°) - azimuth. 0/90/180/270 - north/east/south/west facing for positive GSL.
- Time_Offset (h) - solar time offset from local time.
Variable Inputs
- none
Notes
Calculation of Diffuse.
A simple means of calculating the dffuse clear-sky radiation is given by List (1968) as:
diffuse = 0.5((1-aw-ac)Qa - Id) where
aw = radiation absorbed by water vapour (7%)
ac = radiation absorbed by ozone (2%)
Qa = extra-terrestrial radiation on a horizontal surface at the outer limit of the earth's atmosphere.
Id = direct clear-sky radiation reaching the earth's surface on a horizontal surface.
Optical airmass.
The relative path length of the direct solar beam radiance through the atmosphere. When the sun is directly above a sea-level location the path length is defined as airmass 1 (AM 1.0). AM 1.0 is not synonymous with solar noon because the sun is usually not directly overhead at solar noon in most seasons and locations. When the angle of the sun from zenith (directly overhead) increases, the airmass increases approximately by the secant of the zenith angle. A better calculation (Kasten, F. and A. T. Young (1989). Revised optical air mass tables and approximation formula. Applied Optics 28 (22), 4735-4738) follows:
m = 1.0 / [ cos(Z) + 0.50572 * (96.07995 - Z)-1.6364]
where Z is the solar zenith angle.