cloudfromrad: calculates cloud cover form shortwave radiation

In ilyamaclean/microclima: microclimate modelling with R

calculates cloud cover form shortwave radiation

Description

cloudfromrad is used to derive a cloud cover index as 1 - the ratio of measured to clearksy radiation missing values (e.g. at night) are interpolated

Usage

cloudfromrad(
  rad,
  tme,
  lat,
  long,
  h = 0.00697,
  tc = 15,
  p = 101300,
  G = 2.78,
  Ie = 1352.778,
  merid = round(long/15, 0) * 15,
  dst = 0
)

Arguments

rad	a single numeric value or vector of global solar irradiance(s). Units must be the same as those for Ie. Default is Watts /m^2.
tme	a single value or vector of POSIXlt objects indicating the time(s) for which clearksy radiation is required.
lat	latitude in decimal degrees
long	longitude in decimal degrees
h	a single value or vector of specific humidities (kg kg{-1} ).
tc	a single value or vector of temperatures (ºC).
p	an optional single value or vector of pressures (Pa).
G	an optional single value or vector describing he moisture profile in the atmosphere (per Smith 1966).
Ie	an optional single value for extra-terrestrail radiation to permit adjustment for sun-earth distances (see details).
merid	an optional numeric value representing the longitude (decimal degrees) of the local time zone meridian (0 for GMT). Default is round(long / 15, 0) * 15
dst	an optional numeric value representing the time difference from the timezone meridian (hours, e.g. +1 for BST if merid = 0).

Details

If no values for p are provided, a default value of 101300 Pa, typical of sea-level pressure, is assumed. The method used is that detailed in Crawford & Duchon (1999) Quarterly Journal of the Royal Meteorological Society 122: 1127-1151. The method is not greatly sensitive to humidity, temperature and pressure so approximate values can be provided, or the defaults chosen, if these data are unavailable.

Value

a single value or vector of clearksy radiation.

See Also

The function clearskyrad() is uses to derive clear-sky irradiance. Can be used to derive cloud covers for computing longwave radiation when using longwavetopo() or longwaveveg()

Examples

tme <- as.POSIXlt(c(0:23) * 3600, origin = "2010-05-23 00:00", tz = "GMT")
rad <- clearskyrad(tme, 50, -5, 0.007953766 , 11) * 0.75
cfc <- cloudfromrad(rad, tme, 50, -5, 0.007953766 , 11)
plot(cfc ~ as.POSIXct(tme), type = "l") # should be 0.25

ilyamaclean/microclima documentation built on Oct. 31, 2023, 11:41 p.m.