Functions/Subroutines
real(c_double) function	daylight_hours (domega_s)
	Calculate the number of daylight hours at a location.
elemental real(c_double) function	extraterrestrial_radiation__ra (dlatitude, ddelta, domega_s, ddsubr)
	Calculate extraterrestrial radiation given latitude and time of year.
real(c_double) function	net_shortwave_radiation__rns (drs, dalbedo)
	Calculate net shortwave radiation.
elemental real(c_double) function	solar_declination_simple__delta (idayofyear, inumdaysinyear)
	Calculate the solar declination for a given day of the year.
elemental real(c_double) function	solar_declination__delta (idayofyear, inumdaysinyear)
	Calculate the solar declination for a given day of the year.
elemental real(c_double) function	relative_earth_sun_distance__d_r (idayofyear, inumdaysinyear)
	Calculate the inverse relative Earth-Sun distance for a given day of the year.
elemental real(c_double) function	sunrise_sunset_angle__omega_s (dlatitude, ddelta)
	Calculate sunrise/sunset angle, in RADIANS.
real(c_double) function	solar_radiation_hargreaves__rs (dra, ftmin, ftmax)
	Calculate shortwave solar radiation.
elemental real(c_float) function	estimate_percent_of_possible_sunshine__psun (ftmax, ftmin)
	Estimate percent of possible sunshine.
real(c_double) function	clear_sky_solar_radiation__rso (dra, das, dbs)
	Calculate clear sky solar radiation.
real(c_double) function	clear_sky_solar_radiation_noab__rso (dra, felevation)
	Calculate the clear sky solar radiation.
elemental real(c_double) function	solar_radiation__rs (dra, das, dbs, fpctsun)
	Calculate solar radiation by means of the Angstrom formula.
elemental real(c_double) function	net_longwave_radiation__rnl (ftmin, ftmax, drs, drso)
	Calculate net longwave radiation flux.
elemental real(c_double) function	day_angle__gamma (idayofyear, inumdaysinyear)
	Calculate the day angle in RADIANS.
real(c_double) function	solar_altitude__alpha (dtheta_z)
	Calculate the solar altitude given the zenith angle.
real(c_double) function	zenith_angle__theta_z (dlatitude, ddelta, domega)
	Calculate solar zenith angle given latitude, declination, and (optionally) hour angle.
real(c_double) function	azimuth_angle__psi (ralpha, rlatitude, rdelta)
	Calculate solar azimuth angle.

Variables
real(c_float)	earth_sun_dist_dr
real(c_float)	solar_declination_delta

Function/Subroutine Documentation

◆ azimuth_angle__psi()

real (c_double) function solar_calculations::azimuth_angle__psi	(	real (c_double), intent(in)	ralpha,
		real (c_double), intent(in)	rlatitude,
		real (c_double), intent(in)	rdelta )

Calculate solar azimuth angle.

Parameters

[in]	rAlpha	Solar altitude angle, in RADIANS.
[in]	rLatitude	Latitude of location for which estimate is being made, in RADIANS.
[in]	rDelta	Solar declination angle, in RADIANS.

Return values

rPsi	Solar azimuth angle, in RADIANS.

Note: Implementation follows equation 1.5.2a in Iqbal (1983).; Reference: Iqbal, Muhammad (1983-09-28). An Introduction To Solar Radiation (p. 15). Elsevier Science. Kindle Edition.

Definition at line 597 of file solar_calculations.F90.

◆ clear_sky_solar_radiation__rso()

real (c_double) function solar_calculations::clear_sky_solar_radiation__rso	(	real (c_double), intent(in)	dra,
		real (c_double), intent(in), optional	das,
		real (c_double), intent(in), optional	dbs )

Calculate clear sky solar radiation.

Calculate the clear sky solar radiation (i.e. when rPctSun = 100, n/N=1. Required for computing net longwave radiation.

Parameters

[in]	dRa	Extraterrestrial radiation, in MJ / m**2 / day
[in]	dAs	Solar radiation regression constant, expressing the fraction of extraterrestrial radiation that reaches earth on OVERCAST days.
[in]	sBs	Solar radiation regression constant. As + Bs express the fraction of extraterrestrial radiation that reaches earth on CLEAR days.

Return values

dRso	Clear sky solar radiation, in MJ / m**2 / day

Note: Implementation follows equation 36, Allen and others (1998).; Reference: Allen, R.G., and others, 1998, FAO Irrigation and Drainage Paper No. 56, "Crop Evapotranspiration (Guidelines for computing crop water requirements)", Food and Agriculture Organization, Rome, Italy.

Definition at line 349 of file solar_calculations.F90.

◆ clear_sky_solar_radiation_noab__rso()

real (c_double) function solar_calculations::clear_sky_solar_radiation_noab__rso	(	real (c_double), intent(in)	dra,
		real (c_float), intent(in)	felevation )

Calculate the clear sky solar radiation.

Calculate the clear sky solar radiation (i.e. when rPctSun = 100, n/N=1. Required for computing net longwave radiation. For use when no regression coefficients (A, B) are known.

Parameters

[in]	dRa	Extraterrestrial radiation, in MJ / m**2 / day
[in]	fElevation	Elevation, in METERS above sea level

Return values

dRso	Clear sky solar radiation, in MJ / m**2 / day

Note: Implementation follows equation 37, Allen and others (1998).; Reference: Allen, R.G., and others, 1998, FAO Irrigation and Drainage Paper No. 56, "Crop Evapotranspiration (Guidelines for computing crop water requirements)", Food and Agriculture Organization, Rome, Italy.

Definition at line 397 of file solar_calculations.F90.

◆ day_angle__gamma()

elemental real (c_double) function solar_calculations::day_angle__gamma	(	integer (c_int), intent(in)	idayofyear,
		integer (c_int), intent(in)	inumdaysinyear )

Calculate the day angle in RADIANS.

This function expresses the integer day number as an angle (in radians). Output values range from 0 (on January 1st) to just less than \( 2\pi \) on December 31st.

Parameters

[in]	iDayOfYear	Current day of the year.
[in]	iNumDaysInYear	Number of days in the current year.

Return values

dGamma Day angle in RADIANS.

Note: Implementation follows equation 1.2.2 in Iqbal (1983); Reference: Iqbal, Muhammad (1983-09-28). An Introduction To Solar Radiation (p. 3). Elsevier Science. Kindle Edition.

Definition at line 503 of file solar_calculations.F90.

◆ daylight_hours()

real (c_double) function solar_calculations::daylight_hours ( real (c_double), intent(in) domega_s )

Calculate the number of daylight hours at a location.

Parameters

[in] dOmega_s Sunset hour angle in Radians.

Return values

rN	Number of daylight hours.

Note: Implementation follows equation 34, Allen and others (1998).; Allen, R.G., and others, 1998, FAO Irrigation and Drainage Paper No. 56, "Crop Evapotranspiration (Guidelines for computing crop water requirements)", Food and Agriculture Organization, Rome, Italy.

Definition at line 24 of file solar_calculations.F90.

◆ estimate_percent_of_possible_sunshine__psun()

elemental real (c_float) function solar_calculations::estimate_percent_of_possible_sunshine__psun	(	real (c_float), intent(in)	ftmax,
		real (c_float), intent(in)	ftmin )

Estimate percent of possible sunshine.

This function follows from equation 5 in "The Rational Use of the FAO Blaney-Criddle substituting the rearranged Hargreaves solar radiation formula into equation 5 results in the formulation below

Parameters

[in]	fTMax	Maximum daily air temperature, in °K
[in]	fTMin	Minimum daily air temperature, in °K

Return values

fPsun Percentage of possible sunshine, dimensionless percentage

Todo: [Need to add reference here...]

Definition at line 307 of file solar_calculations.F90.

◆ extraterrestrial_radiation__ra()

elemental real (c_double) function solar_calculations::extraterrestrial_radiation__ra	(	real (c_double), intent(in)	dlatitude,
		real (c_double), intent(in)	ddelta,
		real (c_double), intent(in)	domega_s,
		real (c_double), intent(in)	ddsubr )

Calculate extraterrestrial radiation given latitude and time of year.

Parameters

[in]	dLatitude	Latitude of grid cell in RADIANS.
[in]	dDelta	Solar declination in RADIANS.
[in]	dOmega_s	Sunset hour angle in RADIANS.
[in]	dDsubR	Inverse relative distance Earth-Sun.

Return values

rRa	Extraterrestrial radiation in MJ / m**2 / day.

Note: 1 MJ = 1e6 Joules; 1 Joule = 1 Watt / sec.; Therefore, multiply by 1e6 and divide by 86400 to get W/m*2-day.; Source Equation 21, Allen and others (1998).; Reference Allen, R.G., and others, 1998, FAO Irrigation and Drainage Paper No. 56, "Crop Evapotranspiration (Guidelines for computing crop water requirements)", Food and Agriculture Organization, Rome, Italy.

See also: http://www.fao.org/docrep/x0490e/x0490e07.htm#solar%20radiation

Definition at line 76 of file solar_calculations.F90.

◆ net_longwave_radiation__rnl()

elemental real(c_double) function solar_calculations::net_longwave_radiation__rnl	(	real(c_float), intent(in)	ftmin,
		real(c_float), intent(in)	ftmax,
		real(c_double), intent(in)	drs,
		real(c_double), intent(in)	drso )

Calculate net longwave radiation flux.

Parameters

[in]	fTMin	Minimum daily air temperature, in °C
[in]	fTMax	Maximum daily air temperature, in °C
[in]	dRs	Measured or calculated shortwave solar radiation, in MJ / m**2 / day
[in]	dRso	Calculated clear-sky radiation, in MJ / m**2 / day

Return values

dRnl	Net longwave solar radiation flux (incoming minus outgoing), in MJ / m**2 / day

Note: Implementation follows equation 39, Allen and others (1998).; Reference: Allen, R.G., and others, 1998, FAO Irrigation and Drainage Paper No. 56, "Crop Evapotranspiration (Guidelines for computing crop water requirements)", Food and Agriculture Organization, Rome, Italy.

Definition at line 459 of file solar_calculations.F90.

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◆ net_shortwave_radiation__rns()

real(c_double) function solar_calculations::net_shortwave_radiation__rns	(	real(c_double), intent(in)	drs,
		real(c_double), intent(in)	dalbedo )

Calculate net shortwave radiation.

Parameters

[in]	dRs	Incoming shortwave solar radiation, in MJ / m**2 / day
[in]	dAlbedo	Albedo or canopy reflection coefficient; 0.23 for grass reference crop

Return values

dRns	Net shortwave radiation, in MJ / m**2 / day

Note: Implementation follows equation 38, Allen and others (1998).; Reference: Allen, R.G., and others, 1998, FAO Irrigation and Drainage Paper No. 56, "Crop Evapotranspiration (Guidelines for computing crop water requirements)", Food and Agriculture Organization, Rome, Italy.

Definition at line 112 of file solar_calculations.F90.

◆ relative_earth_sun_distance__d_r()

elemental real (c_double) function solar_calculations::relative_earth_sun_distance__d_r	(	integer (c_int), intent(in)	idayofyear,
		integer (c_int), intent(in)	inumdaysinyear )

Calculate the inverse relative Earth-Sun distance for a given day of the year.

Parameters

[in]	iDayOfYear	Integer day of the year (January 1 = 1)
[in]	iNumDaysInYear	Number of days in the current year

Return values

dDsubR Relative Earth-Sun distance

Note: Implementation follows equation 23, Allen and others (1998):
\( d_r = 1 + 0.033 \cos \left( \frac{ 2 \pi }{365} J \right) \)

where:
\( d_r \) is the inverse relative distance between Earth and the Sun
\( J \) is the current day of the year; References: Allen, R.G., and others, 1998, FAO Irrigation and Drainage Paper No. 56, "Crop Evapotranspiration (Guidelines for computing crop water requirements)", Food and Agriculture Organization, Rome, Italy.; Duffie, J.A., Beckman, W.A. Solar Engineering of Thermal Processes. New York: Wiley, 1980.; Equation 1.2.3 in Iqbal, Muhammad (1983-09-28). An Introduction To Solar Radiation (p. 28). Elsevier Science. Kindle Edition.

Definition at line 214 of file solar_calculations.F90.

◆ solar_altitude__alpha()

real (c_double) function solar_calculations::solar_altitude__alpha ( real (c_double), intent(in) dtheta_z )

Calculate the solar altitude given the zenith angle.

Parameters

[in] rTheta_z Solar zenith angle for given location and time, in RADIANS

Return values

rAlpha Solar altitude angle for given location and time, in RADIANS

Definition at line 522 of file solar_calculations.F90.

◆ solar_declination__delta()

elemental real (c_double) function solar_calculations::solar_declination__delta	(	integer (c_int), intent(in)	idayofyear,
		integer (c_int), intent(in)	inumdaysinyear )

Calculate the solar declination for a given day of the year.

Parameters

[in]	iDayOfYear	Integer day of the year (January 1 = 1)
[in]	iNumDaysInYear	Number of days in the current year

Return values

dDelta Solar declination, in RADIANS

Note: Implementation follows equation 1.3.1 in Iqbal (1983).; Iqbal (1983) reports maximum error of 0.0006 radians; if the last two terms are omitted, the reported accuracy drops to 0.0035 radians.; Reference: Iqbal, Muhammad (1983-09-28). An Introduction To Solar Radiation (p. 10). Elsevier Science. Kindle Edition.

Definition at line 167 of file solar_calculations.F90.

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◆ solar_declination_simple__delta()

elemental real (c_double) function solar_calculations::solar_declination_simple__delta	(	integer (c_int), intent(in)	idayofyear,
		integer (c_int), intent(in)	inumdaysinyear )

Calculate the solar declination for a given day of the year.

Parameters

[in]	iDayOfYear	Integer day of the year (January 1 = 1)
[in]	iNumDaysInYear	Number of days in the current year

Return values

dDelta Solar declination, in RADIANS

Note: Implementation follows equation XXX? in:; Allen, R.G., and others, 1998, FAO Irrigation and Drainage Paper No. 56, "Crop Evapotranspiration (Guidelines for computing crop water requirements)", Food and Agriculture Organization, Rome, Italy.

Definition at line 138 of file solar_calculations.F90.

◆ solar_radiation__rs()

elemental real (c_double) function solar_calculations::solar_radiation__rs	(	real (c_double), intent(in)	dra,
		real (c_double), intent(in)	das,
		real (c_double), intent(in)	dbs,
		real (c_double), intent(in)	fpctsun )

Calculate solar radiation by means of the Angstrom formula.

Parameters

[in]	dRa	Extraterrestrial radiation in MJ / m**2 / day
[in]	dAs	Solar radiation regression constant, expressing the fraction of extraterrestrial radiation that reaches earth on OVERCAST days.
[in]	dBs	Solar radiation regression constant. As + Bs express the fraction of extraterrestrial radiation that reaches earth on CLEAR days.
[in]	fPctSun	Percent of TOTAL number of sunshine hours during which the sun actually shown.

Return values

fRs	Solar radiation in MJ / m**2 / day

@notes Implementation follows equation 35, Allen and others (1998).

Reference: Allen, R.G., and others, 1998, FAO Irrigation and Drainage Paper No. 56, "Crop Evapotranspiration (Guidelines for computing crop water requirements)", Food and Agriculture Organization, Rome, Italy.

Definition at line 428 of file solar_calculations.F90.

◆ solar_radiation_hargreaves__rs()

real (c_double) function solar_calculations::solar_radiation_hargreaves__rs	(	real (c_double), intent(in)	dra,
		real (c_float), intent(in)	ftmin,
		real (c_float), intent(in)	ftmax )

Calculate shortwave solar radiation.

Calculates the solar radiation using Hargreave's radiation formula. For use when percent possible daily sunshine value is not available.

Parameters

[in]	dRa	Extraterrestrial radiation, in MJ / m**2 / day
[in]	rTMin	Minimum daily air temperature, in °C
[in]	rTMax	Maximum daily air temperature, in °C

Return values

dRa	Solar radiation, in MJ / m**2 / day

Note: Implementation follows equation 50, Allen and others (1998).; Reference: Allen, R.G., and others, 1998, FAO Irrigation and Drainage Paper No. 56, "Crop Evapotranspiration (Guidelines for computing crop water requirements)", Food and Agriculture Organization, Rome, Italy.

Definition at line 274 of file solar_calculations.F90.

◆ sunrise_sunset_angle__omega_s()

elemental real (c_double) function solar_calculations::sunrise_sunset_angle__omega_s	(	real (c_double), intent(in)	dlatitude,
		real (c_double), intent(in)	ddelta )

Calculate sunrise/sunset angle, in RADIANS.

Parameters

[in]	dLatitude	Latitude, in RADIANS
[in]	dDelta	Solar declination, in RADIANS

Return values

dOmega_s Sunset angle, in RADIANS

Note: Implementation follows equation 25, Allen and others (1998).; Hour angle is zero at solar noon. Definition in Iqbal (1983) yields positive values before solar noon, and negative values following solar noon.; Reference: Allen, R.G., and others, 1998, FAO Irrigation and Drainage Paper No. 56, "Crop Evapotranspiration (Guidelines for computing crop water requirements)", Food and Agriculture Organization, Rome, Italy.

Definition at line 245 of file solar_calculations.F90.

◆ zenith_angle__theta_z()

real (c_double) function solar_calculations::zenith_angle__theta_z	(	real (c_double), intent(in)	dlatitude,
		real (c_double), intent(in)	ddelta,
		real (c_double), intent(in), optional	domega )

Calculate solar zenith angle given latitude, declination, and (optionally) hour angle.

Calculate solar zenith. Solar zenith angle is the angle between a point directly overhead and the center of the sun's disk.

Parameters

[in]	rLatitude	Latitude of location for which estimate is being made, in RADIANS
[in]	rDelta	Solar declination angle, in RADIANS
[in]	rOmega	[OPTIONAL] Hour angle, measured at the celestial pole between the observer's meridian and the solar meridian, in RADIANS.

Return values

rTheta_z Solar zenith angle for given location and time, in RADIANS

Note: Implementation follows equation 9.67, Jacobson, 2005; Reference: Jacobson, M.Z., 2005, Fundamentals of atmospheric modeling, Second Edition: Cambridge University Press.

Definition at line 557 of file solar_calculations.F90.

Variable Documentation

◆ earth_sun_dist_dr

real (c_float) solar_calculations::earth_sun_dist_dr

Definition at line 9 of file solar_calculations.F90.

◆ solar_declination_delta

real (c_float) solar_calculations::solar_declination_delta

Definition at line 10 of file solar_calculations.F90.

Functions/Subroutines

Variables

Function/Subroutine Documentation

◆ azimuth_angle__psi()

◆ clear_sky_solar_radiation__rso()

◆ clear_sky_solar_radiation_noab__rso()

◆ day_angle__gamma()

◆ daylight_hours()

◆ estimate_percent_of_possible_sunshine__psun()

◆ extraterrestrial_radiation__ra()

◆ net_longwave_radiation__rnl()

◆ net_shortwave_radiation__rns()

◆ relative_earth_sun_distance__d_r()

◆ solar_altitude__alpha()

◆ solar_declination__delta()

◆ solar_declination_simple__delta()

◆ solar_radiation__rs()

◆ solar_radiation_hargreaves__rs()

◆ sunrise_sunset_angle__omega_s()

◆ zenith_angle__theta_z()

Variable Documentation

◆ earth_sun_dist_dr

◆ solar_declination_delta