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radsol_clrsky_fao56

Compute clear sky solar radiation as described in FAO 56.

Available in version 6.4.0 and later.

Prototype

load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/crop.ncl"  ; This library is automatically loaded
                                                      ; from NCL V6.5.0 onward.
                                                      ; No need for user to explicitly load.

	function radsol_clrsky_fao56 (
		radext  : numeric,  
		opt [1] : logical   
	)

Arguments

radext

A scalar or multidimensional array containing extraterrestrial radiation.

opt

opt - A scalar logical value to which attributes may be associated.

opt=False means no options are set. Use default values: (a) The default as and bs are set to the FAO recommended values: as=0.25 and bs=0.50
(b) The z value is set to 0.0

opt=True means there are several parameters that can be set.

opt@as - user specifies the coefficient
opt@bs - user specifies the coefficient
opt@z - user specifies the elevations

Return value

An array of the same size, shape and units as radext.

Description

Computes clear sky solar radiation based upon the input radext as specified in the Food and Agriculture Organization (FAO) Irrigation and Drainage Paper 56 entitled: Crop evapotranspiration - Guidelines for computing crop water requirement. Specifically, see equation 36 or 37 of Chapter 3.

Examples

Example 1: Replicate example 10 in Chapter 3.

  jday   = 135 
  lat    = -22.9        ; Rio de Janeiro, Brazil
  radext = radext_fao56(jday, lat, 1)           ;  25.111 MJ/(m2-day) 
  radclr = radsol_clrsky_fao56(radext, False)   ;  18.833 MJ/(m2-day) 
  printVarSummary(radclr)

The output for 'radsol'is

     Variable: rs135_1
     Type: float
     Total Size: 4 bytes
                 1 values
     Number of Dimensions: 1
     Dimensions and sizes:	[1]
     Coordinates: 
     Number Of Attributes: 5
       long_name :	clear sky radiation
       units :	MJ/(m2-day)
       url :	http://www.fao.org/docrep/X0490E/x0490e07.htm
       info :	FAO 56; EQN 36
       parameters :	as=0.25  bs=0.5
     
     (0)	18.83327

Example 2: Consider RADEXT(jday,lat); compute solar clear sky radiation.

  lat     = (/ -22.9, 0, 45 /)
  lat@units = "degrees_north"
  lat!0   = "lat"
  lat&lat =  lat

  time    = (/ 15, 135, 246, 306 /)
  time@long_name = "julian day"
  time!0    = "time"
  time&time =  time  

  RADEXT = radext_fao56(time, lat, 1)    ;  MJ/(m2-day) 
  RADCLR = radsol_clrsky_fao56(RADEXT, False)   ;  MJ/(m2-day) 
  printVarSummary(RADCLR)

The output for 'radsol' is