Angstrom-Prescott model is used to calculate daily global irradiance for a horizontal surface based on sunshine duration.
Usage
ap(days, lat, extraT=NULL, A, B, SSD)
Arguments
days
Vector of class 'Date' of length n.
lat
Latitude in decimal degrees.
extraT
Optional. Vector of length n of extraterrestrial solar radiation [MJm-2]. If 'NULL' then it is calculated by the function. Providing extraterrestrial solar radiation speeds up the computation
A
Angstrom-Prescott model 'A' coefficient.
B
Angstrom-Prescott model 'B' coefficient.
SSD
Vector of length n containing sunshine duration [in hours].
Value
Vector of length n of daily solar radiation [MJm-2].
Details
Model proposed by Angstrom (1924) and modified by Prescott (1940) assumed linear relationship between: (1) a proportion of bright sunshine hours and astronomical day length and (2) proportion of incoming daily global solar radiation and daily extra-terrestrial radiation. This linear relationship is described by empirical model coefficients: A - intercept, B - slope. Both astronomical day length and daily extra-terrestrial radiation are calculated within this function based on location and time.
References
Angstrom, A., 1924. Solar and terrestrial radiation. Quarterly Journal of the Royal Meteorological Society, 50:121-125.
Prescott, J.A., 1940. Evaporation from a water surface in relation to solar radiation. Transactions of the Royal Society of South Australia, 64:114-118.
require(zoo)
data(Metdata)
A <- 0.21
B <- 0.57
sunshine <- Metdata$meteo$SUNSHINE
days <- Metdata$meteo$DAY
lat <- Metdata$LATITUDE
plot(zoo(ap(days,lat,extraT=NULL,A,B,sunshine),order.by=days))