R_a: Radiation, extraterrestrial solar
In WDNR-Water-Use/CSLSevap: Evapo(transpi)ration Calculations

Description Usage Arguments Value References

Calculates the extraterrestrial radiation for a given location and timestep. For daily periods, uses Equation 21 from Allen et al. (1998). For hourly or shorter periods, uses Equation 28 from Allen et al. (1998).

1	R_a(dt, datetimes, phi, Lm, Lz, Gsc = 0.082)

`dt`	a string indicating the timestep of calculation. If not "hourly", assumes a daily or larger timestep
`datetimes`	timeseries of datetimes to use in calculations POSIXct
`phi`	latitude of the location (radians). Positive for northern hemisphere, negative for southern hemisphere.
`Lm`	longitude of the measurement site (degrees west of Greenwich).
`Lz`	longitude of the center of the time zone used for measurements (degrees west of Greenwich). For example, Lz = 75, 90, 105 and 120° for the Eastern, Central, Rocky Mountain and Pacific time zones (United States) and Lz = 0° for Greenwich, 330° for Cairo (Egypt), and 255° for Bangkok (Thailand).
`Gsc`	solar constant (MJ/m^2/min). Defaults to 0.0820 MJ/m^2/min.

`Ra`	extraterrestrial radiation (MJ/m^2/day) or (MJ/m^2/hour), depending on length of input time period

Allen, R. G., Pereira, L. S., Raes, D., & Smith, M. (1998). Crop evapotranspiration: Guidelines for computing crop water requirements. Rome: FAO. Retrieved from http://www.fao.org/docrep/X0490E/x0490e00.htm.

WDNR-Water-Use/CSLSevap documentation built on April 9, 2021, 1:35 a.m.