Rn {MeTo}

Net radiation (Rn)

Description

Difference between the incoming net shortwave radiation (Rns) and the outgoing net longwave radiation (Rnl).

Usage

Rn(
  x,
  Tmax = NULL,
  Tmin = NULL,
  Rhmax = NULL,
  Rhmin = NULL,
  Rs = NULL,
  n = NULL,
  elev,
  lat.rad = NULL,
  lat.deg = NULL,
  long.deg = NULL,
  Rhmean = NULL,
  actVP = NULL,
  Tmean = NULL,
  tl,
  control = list()
)

Arguments

x

date-time object or day of the year (must be date-time object if calculation period is shorter than a day)

Tmax

maximum temperature [degreeC] during 24-hour period (for daily values)

Tmin

minimum temperature [degreeC] during 24-hour 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 30-minute period or 24 for daily period). Only needed if x is date-time object with length of 1.

control

list for control parameters and empirical factors (see Details)

Details

for daily and hourly calculations

x:

must be provided as.numeric (1-366) or as a common date-time object (e.g, POSIXct, POSIXlt or Date objects). All formats for which is.timepoint from the lubridate package returns TRUE can be used

control:

albedo: default 0.23 for the hypothetical grass and alfalfa reference crops used in the FAO-56 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)

Value

net radiation

Note

eq. 40 of reference

References

Allen, R. G., Pereira, L. S., Raes, D., & Smith, M. (1998). Crop evapotranspiration-Guidelines for computing crop water requirements-FAO Irrigation and drainage paper 56. FAO, Rome, 300(9).

See Also

Rns, Rnl

Examples

# --------------------------------------------
#  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('2018-10-01 14:30', '2018-10-01 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('2018-10-01 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))