clearskyrad: calculates clearsky radiation

In dklinges9/mcera5: Tools to Acquire and Process ERA5 Data for Use in Microclimate Modelling

calculates clearsky radiation

Description

'clearskyrad' is used to calculate clear-sky shortwave irradiance using the Crawford & Duchon (1999) method

Usage

clearskyrad(
  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

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	an optional single value or vector of specific humidities (kg kg{-1} ).
tc	an optional 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

The units returned are the same as for 'Ie', with the default option in W / M^2. 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 [cloudfromrad()] uses this function to return 1 - ratio of measured to clearsky radiation for input when computing longwave radiation when using [longwavetopo()] or [longwaveveg()]

Examples

tme <- as.POSIXlt(c(0:23) * 3600, origin = "2010-05-23 00:00", tz = "GMT")
Io <- clearskyrad(tme, 50, -5, 0.007953766 , 11)
plot(Io ~ as.POSIXct(tme), type = "l")

dklinges9/mcera5 documentation built on March 1, 2024, 11:40 p.m.