ap {sirad}

Angstrom-Prescott solar radiation model

Description

Angstrom-Prescott model is used to calculate daily global irradiance for a horizontal surface based on sunshine duration.

Usage

ap(days, lat, lon, extraT=NULL, A=NA, B=NA, SSD)

Arguments

days

Vector of class 'Date' of length n.

lat

Latitude in decimal degrees.

lon

Longitude 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. If 'NA' then A is derived from the map of interpolated coefficients estimated from Meteosat solar radiation data. See details.

B

Angstrom-Prescott model 'B' coefficient. If 'NA' then B is derived from the map of interpolated coefficients estimated from Meteosat solar radiation data. See details.

SSD

Vector of length n containing sunshine duration [in hours].

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. Model coefficients A and B (if not provided) are derived from interpolated Meteosat-based coefficients from Bojanowski et al. 2013.

Value

Vector of length n of daily solar radiation [MJm-2].

Note

SSD input can contain NA's, but length of vectors 'SSD' and 'days' has to be the identical.

Author(s)

Jedrzej S. Bojanowski

References

Bojanowski, J.S., Vrieling, A., Skidmore, A.K., 2013. Calibration of solar radiation models for Europe using Meteosat Second Generation and weather station data. Agricultural and Forest Meteorology 176:1-9.
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.

See Also

'apcal' to calibrate the model

Examples

require(zoo)
#A <- 0.21
#B <- 0.57
sunshine <- Metdata$meteo$SUNSHINE
days <- Metdata$meteo$DAY
lat <- Metdata$LATITUDE
lon <- Metdata$LONGITUDE
plot(zoo(ap(days,lat,lon, extraT=NULL,A=NA,B=NA,sunshine),order.by=days))