Daily inward shortwave solar radiation.

Daily inward shortwave solar radiation at crop surface [MJ m-2 day-1] by providing sunshine duration (SSD) in hours or cloud cover in fraction.

cal_Rsi(lat, J, ssd = NULL, cld = NULL, Z = 0, a = 0.25, b = 0.5)

Arguments

lat

Latitude [degree].

J

day of year

ssd

sunshine duration hours. If ssd = NULL, Rsi is the clear-sky solar radiation.

cld

Cloud cover [fraction]. If provided it would be directly used to calculate solar radiation rather than SSD and parameter a and b.

Z

elevation (m)

a

Coefficient of the Angstrom formula. Determine the relationship between ssd and radiation. Default 0.25.

b

Coefficient of the Angstrom formula. Default 0.50.

Value

A data.table, solar radiation at crop surface [MJ m-2 day-1].

  • Rsi_toa: Clear-sky surface downward shortwave radiation

  • Rsi: Surface downward shortwave radiation

References

  1. Martinezlozano J A, Tena F, Onrubia J E, et al. The historical evolution of the Angstrom formula and its modifications: review and bibliography.J. Agricultural & Forest Meteorology, 1985, 33(2):109-128.

  2. https://github.com/sbegueria/SPEI/blob/master/R/penman.R