Description Usage Arguments Details Value Note References See Also Examples
Difference between the incoming net shortwave radiation (Rns
) and the outgoing net longwave radiation (Rnl
).
1 2 3 4 
x 
datetime object or day of the year (must be datetime object if calculation period is shorter than a day) 
Tmax 
maximum temperature [degreeC] during 24hour period (for daily values) 
Tmin 
minimum temperature [degreeC] during 24hour period (for daily values) 
Rhmax 
daily maximum of air humidity [percent] (for daily values) 
Rhmin 
daily minimum of air humidity [percent] (for daily values) 
Rs 
incoming solar radiation [MJ/(m2 time)] 
n 
Actual hours of sunshine. Used to calculate Rs if missing. 
elev 
station elevation above sea level [m] 
lat.rad 
latitude [rad]. Use either lat.rad or lat.deg. Latitude is positive for the northern hemisphere and negative for the southern hemisphere 
lat.deg 
latitude [degree]. Use either lat.deg or lat.rad. Latitude is positive for the northern hemisphere and negative for the southern hemisphere 
long.deg 
longitude of the measurement site (degrees east of Greenwich) (for periods < 1 day) 
Rhmean 
Mean air humidity [percent] for periods < day or if Rhmax and Rhmin are missing 
actVP 
Actual vapor pressure [kPa]. If Rhmax, Rhmin and Rhmean are NULL 
Tmean 
Mean air temperature [degree C] for periods < day 
tl 
length of calculation period [hour] (1 for hourly period, 0.5 for a 30minute period or 24 for daily period). Only needed if x is datetime object with length of 1. 
control 
list for control parameters and empirical factors (see Details) 
for daily and hourly calculations
must be provided as.numeric (1366) or as a common datetime object (e.g, POSIXct, POSIXlt or Date objects). All formats for which is.timepoint from the lubridate package returns TRUE can be used
albedo: default 0.23 for the hypothetical grass and alfalfa reference crops used in the FAO56 PM equations
as: regression constant, expressing fraction of extraterrestrial radiation reaching earth on overcast days (n = 0) (default = 0.25)
bs: as + bs fraction of extraterrestrial radiation reaching earth on clear days (n = N) (default = 0.5)
net radiation
eq. 40 of reference
Allen, R. G., Pereira, L. S., Raes, D., & Smith, M. (1998). Crop evapotranspirationGuidelines for computing crop water requirementsFAO Irrigation and drainage paper 56. FAO, Rome, 300(9).
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20  # 
# Daily period
# 
Rn(x = 105, n = 8.5, elev = 2, actVP = 2.85, Tmax = 34.8,
Tmin = 25.6, lat.deg = 13.73)
Rn(x = 135, elev = 1, Rs = 14.5, Tmax = 25.1, Tmin = 19.1,
lat.deg = 22.9, actVP = 2.1)
# 
# Hourly period
# 
Rn(x = as.POSIXct(c('20181001 14:30', '20181001 15:30')), Tmean = c(38, 37.8),
Rhmean = c(52, 52.2), Rs = c(2.450, 2.1), elev = 8, lat.deg = 16.2,
long.deg = 343.75, control = list(Lz = 15))
Rn(x = as.POSIXct('20181001 14:30'), Tmean = 38, Rhmean = 52, tl = 1, Rs = 2.450,
elev = 8, lat.deg = 16.2, long.deg = 343.75, control = list(Lz = 15))

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