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radsol3_hargreaves_fao56

Compute solar radiation derived from air temperature differences using Hargreaves method 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 radsol3_hargreaves_fao56 (
		tmin       : numeric,  
		tmax       : numeric,  
		radext     : numeric,  
		krs        : numeric,  
		iounit [3] : integer   
	)

Arguments

tmin
tmax

Scalars or arrays of any dimensionality containing minimum and maximum temperatures.

radext

Scalar or array containing extraterrestrial radiation. Must have the same dimensionality as tmin and tmax.

krs

Adjustment coefficient [ 0.16 - 0.19 ]. May be a scalar or an array of the same dimensionality as tmin, tmax and radext.

iounit

An integer array of length 3 indicating the units of input arguments and the units of the returned argument.

iounit(0)=0 ; input tmin and tmax are in degrees C (degC).
iounit(0)=1 ; input tmin and tmax are in degrees K (degK).
iounit(0)=2 ; input tmin and tmax are in degrees F.

iounit(1)=0 ; input radext are in mm/day
iounit(1)=1 ; input radext are in MJ/(m2-day)
iounit(1)=2 ; input radext are in W/m2

iounit(2)=0 ; output units => mm/day
iounit(2)=1 ; output units => MJ/(m2-day)
iounit(2)=2 ; output units => W/m2

If iounit(0)=1 or 2, the tmin, tmax will be converted to degC internally prior to the computation. The input arguments are unaltered.

If iounit(1)=0 or 2, the radext will be converted to MJ/(m2-day) internally prior to the computation. The input arguments are unaltered.

Return value

An array with the same dimensionality and type as tmin, tmin and radext containing estimated solar radiation.

Description

Compute solar radiation derived from air temperature difference using Hargreaves method as described in the Food and Agriculture Organization (FAO) Irrigation and Drainage Paper 56 entitled: Crop evapotranspiration - Guidelines for computing crop water requirement . Specifically, see equation 50 of Chapter 3.

Examples

Example 1: Replicate example 15 in Chapter 3 in Chapter 3. Here,

iounit(0)=0 because tmin and tmax are degC
iounit(1)=1 because radext are "MJ/(m2-day)"
iounit(2)=1 are set to different values to illustrate different units of the returned variable

  jday   = 196
  lat    = 45.72
  radext = radext_fao56(jday, lat, 1)   ; 40.55 MJ/(m2-day)

  krs  = 0.16
  tmin = 14.8
  tmax = 26.6
  radsol_hg0 = radsol3_hargreaves_fao56(tmin, tmax, radext, krs, (/0,1,0/) )  ; 9.09 mm/day
  radsol_hg1 = radsol3_hargreaves_fao56(tmin, tmax, radext, krs, (/0,1,1/) )  ; 22.29 MJ/(m2-day)
  radsol_hg2 = radsol3_hargreaves_fao56(tmin, tmax, radext, krs, (/0,1,2/) )  ; 257.98 W/m2

The output for 'radsol_hg1' is

Variable: radsol_hg1
Type: float
Total Size: 4 bytes
            1 values
Number of Dimensions: 1
Dimensions and sizes:   [1]
Coordinates: 
Number Of Attributes: 4
  long_name :   Hargreaves solar radiation
  units :       MJ/(m2-day)
  url : http://www.fao.org/docrep/X0490E/x0490e07.htm
  info :        FAQ 56: EQN 50
(0)     22.28951

Example 2: Consider TMIN, TMAX, RADEXT of shape and size (time,lat,lon) with sizes (3,73,144).

  RADSOL_HG1 = radsol3_hargreaves_fao56(TMIN, TMAX, RADEXT, krs, (/0,1,1/) )  ; 22.29 MJ/(m2-day)
  printVarSummary(RADSOL_HG1)

The output for 'RADSOL_HG1' is