`radiation.Rd`

Set of functions used in the calculation of incoming solar radiation and net radiation.

```
radiation_dateStringToJulianDays(dateStrings)
radiation_daylength(latrad, slorad, asprad, delta)
radiation_daylengthseconds(latrad, slorad, asprad, delta)
radiation_directDiffuseInstant(solarConstant, latrad, slorad, asprad, delta,
hrad, R_s, clearday)
radiation_directDiffuseDay(solarConstant, latrad, slorad, asprad, delta,
R_s, clearday, nsteps = 24)
radiation_potentialRadiation(solarConstant, latrad, slorad, asprad, delta)
radiation_julianDay(year, month, day)
radiation_skyLongwaveRadiation(Tair, vpa, c)
radiation_outgoingLongwaveRadiation(solarConstant, latrad, elevation, slorad,
asprad, delta, vpa, tmin, tmax, R_s)
radiation_netRadiation(solarConstant, latrad, elevation, slorad, asprad, delta,
vpa, tmin, tmax, R_s, alpha = 0.08)
radiation_solarConstant(J)
radiation_solarDeclination(J)
radiation_solarElevation(latrad, delta, hrad)
radiation_solarRadiation(solarConstant, latrad, elevation, slorad, asprad, delta,
diffTemp, diffTempMonth, vpa, precipitation)
radiation_sunRiseSet(latrad, slorad, asprad, delta)
```

- dateStrings
A character vector with dates in format "YYYY-MM-DD".

- latrad
Latitude (in radians North).

- slorad
Slope (in radians).

- asprad
Aspect (in radians from North).

- delta
Solar declination (in radians).

- solarConstant
Solar constant (in kW·m-2).

- hrad
Solar hour (in radians).

- R_s
Daily incident solar radiation (MJ·m-2).

- clearday
Boolean flag to indicate a clearsky day (vs. overcast).

- nsteps
Number of daily substeps.

- J
Julian day (integer), number of days since January 1, 4713 BCE at noon UTC.

- year, month, day
Year, month and day as integers.

- alpha
Surface albedo (from 0 to 1).

- Tair
Air temperature (in degrees Celsius).

- vpa
Average daily vapor pressure (kPa).

- c
Proportion of sky covered by clouds [0-1].

- tmin, tmax
Minimum and maximum daily temperature (ºC).

- elevation
Elevation above sea level (in m).

- precipitation
Precipitation (in mm).

- diffTemp
Difference between maximum and minimum temperature (ºC).

- diffTempMonth
Difference between maximum and minimum temperature, averaged over 30 days (ºC).

Values returned for each function are:

`radiation_dateStringToJulianDays`

: A vector of Julian days (i.e. number of days since January 1, 4713 BCE at noon UTC).`radiation_daylength`

: Day length (in hours).`radiation_daylengthseconds`

: Day length (in seconds).`radiation_directDiffuseInstant`

: A vector with instantaneous direct and diffusive radiation rates (for both SWR and PAR).`radiation_directDiffuseDay`

: A data frame with instantaneous direct and diffusive radiation rates (for both SWR and PAR) for each subdaily time step.`radiation_potentialRadiation`

: Daily (potential) solar radiation (in MJ·m-2).`radiation_julianDay`

: Number of days since January 1, 4713 BCE at noon UTC.`radiation_skyLongwaveRadiation`

: Instantaneous incoming (sky) longwave radiation (W·m-2).`radiation_outgoingLongwaveRadiation`

: Daily outgoing longwave radiation (MJ·m-2·day-1).`radiation_netRadiation`

: Daily net solar radiation (MJ·m-2·day-1).`radiation_solarConstant`

: Solar constant (in kW·m-2).`radiation_solarDeclination`

: Solar declination (in radians).`radiation_solarElevation`

: Angle of elevation of the sun with respect to the horizon (in radians).`radiation_solarRadiation`

: Daily incident solar radiation (MJ·m-2·day-1).`radiation_sunRiseSet`

: Sunrise and sunset hours in hour angle (radians).

Code for `radiation_julianDay()`

, `radiation_solarConstant()`

and `radiation_solarDeclination()`

was translated to C++ from R code in package 'insol' (by J. G. Corripio).

Danby, J. M. Eqn. 6.16.4 in Fundamentals of Celestial Mechanics, 2nd ed. Richmond, VA: Willmann-Bell, p. 207, 1988.

Garnier, B.J., Ohmura, A., 1968. A method of calculating the direct shortwave radiation income of slopes. J. Appl. Meteorol. 7: 796-800

McMahon, T. A., M. C. Peel, L. Lowe, R. Srikanthan, and T. R. McVicar. 2013. Estimating actual, potential, reference crop and pan evaporation using standard meteorological data: a pragmatic synthesis. Hydrology & Earth System Sciences 17:1331–1363. See also: http://www.fao.org/docrep/x0490e/x0490e06.htm.

Reda, I. and Andreas, A. 2003. Solar Position Algorithm for Solar Radiation Applications. 55 pp.; NREL Report No. TP-560-34302, Revised January 2008. http://www.nrel.gov/docs/fy08osti/34302.pdf

Spitters, C.J.T., Toussaint, H.A.J.M. and Goudriaan, J. (1986). Separating the diffuse and direct components of global radiation and its implications for modeling canopy photosynthesis. I. Components of incoming radiation. Agricultural and Forest Meteorology, 38, 231–242.