Rnl: Net longwave radiation (Rnl)

Description Usage Arguments Details Value Note References

Description

Net longwave radiation (Rnl).

Usage

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Rnl(x, Tmax = NULL, Tmin = NULL, Rhmax = NULL, Rhmin = NULL,
  Rs = NULL, lat.rad = NULL, lat.deg = NULL, long.deg = NULL, elev,
  actVP = NULL, tl, Tmean = NULL, Rhmean = NULL, 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)]

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

see Rso

elev

station elevation above sea level [m]

actVP

Actual vapor pressure [kPa]. If Rhmax, Rhmin and Rhmean are NULL

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 length of x is date-time object with length of 1.

Tmean

mean temperature [degreeC] during the time period (for periods shorter than a day)

Rhmean

Mean air humidity [percent] (for periods shorter than a day or if Rhmax and Rhmin are missing)

control

list for control parameters and empirical factors (see Details and controlDefaults)

Details

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:

Lz:
longitude of the centre of the local time zone (degrees west of Greenwich)
- 0 for Greenwich
- 345 for Germany
- 330 for Cairo (Egypt)
- 255 for Bangkok (Thailand)
- 75, 90, 105 and 120 for Eastern, Central, Rocky Mountain and Pacific time zones (United States)
Lz is only needed if calculation period is shorter 1 day.

est.ratio.Rs.Rso:
Rs/Rso is used to represent cloud cover. For hourly or shorter periods during the nighttime, the ratio Rs/Rso is set equal to the Rs/Rso calculated for a time period occurring 2-3 hours before sunset. If single values during nighttime are calculated Rs/Rso ration 2-3 hours before sunset can not be calculated and an approximation is needed. Following Allen (1999) one can assume Rs/Rso = 0.4 to 0.6 during nighttime periods in humid and subhumid climates and Rs/Rso = 0.7 to 0.8 in arid and semiarid climates. A value of Rs/Rso = 0.3 presumes total cloud cover.

Value

Rnl net outgoing longwave radiation [MJ(/m2 time)]

Note

eq. 39 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).


MeTo documentation built on May 2, 2019, 3:47 p.m.