NCL Website header
NCL Home > Documentation > Functions > Meteorology, Crop

u2_fao56

Compute 2-meter wind speed (m/s) as described in FAO 56.

Available in version 6.4.0 and later.

Prototype

load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/crop.ncl"

	function u2_fao56 (
		uz        : numeric,  
		z         : integer,  
		wunit [2] : integer   
	)

Arguments

uz

A scalar or array of any dimensionality containing wind speed at a height of z meters. See wunit description.

z

A variable of the same size and shape as uz containing the height(m) of uz above ground surface.

wunit

An array of length 2 which specifies the units of the input uz and the output 2m wind speed:

  • wunit(0)=0 ; input uz are m/s
  • wunit(0)=1 ; input uz are km/hr
  • wunit(0)=2 ; input uz are mph
  • wunit(1)=0 ; output u2 are m/s
  • wunit(1)=1 ; output u2 are km/hr
  • wunit(1)=2 ; output u2 are mph

Return value

An array with the same dimensionality and type as uz containing estimated 2-meter wind speeds (m/s).

Description

Compute 2-meter wind speed (m/s) 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 47 of Chapter 3.

If necessary, the input uz will be converted to (m/s). The input uz are not changed.

See Also

Crop & Evapotranspiration functions

Examples

Example 1: Replicate example 14 in Chapter 3 in Chapter 3.

  uz  =  3.2                        ; m/s
  z   = 10.0                        ; m

  u2_00 = u2_fao56(uz, z, (/0,0/))   ; 2.39 m/s 
  u2_01 = u2_fao56(uz, z, (/0,1/))   ; 8.62 km/hr
  u2_02 = u2_fao56(uz, z, (/0,2/))   ; 5.35 mph 
  printVarSummary(u2)

The output for 'u2_00' is

     Variable: u2
     Type: float
     Total Size: 4 bytes
                 1 values
     Number of Dimensions: 1
     Dimensions and sizes:	[1]
     Coordinates: 
     Number Of Attributes: 4
       long_name :	Estimated 2-meter wind speed
       units :	m/s
       url :	http://www.fao.org/docrep/X0490E/x0490e07.htm
       info :	FAO 56; EQN 47

Example 2: Consider UZ(time,lat,lon) and Z(time,lat,lon) with sizes (3,73,144).

  U2  = u2_fao56(UZ, Z,  (/0,0/))  
  printVarSummary(U2)

The output for 'U2' is

     Variable: U2
     Type: float
     Total Size: 126144 bytes
                 31536 values
     Number of Dimensions: 3
     Dimensions and sizes:	[time | 3] x [lat | 73] x [lon | 144]
     Coordinates: 
                 time: [1..3]
                 lat: [-90..90]
                 lon: [ 0..357.5]
     Number Of Attributes: 4
       long_name :	Estimated 2-meter wind speed
       units :	m/s
       url :	http://www.fao.org/docrep/X0490E/x0490e07.htm
       info :	FAO 56; EQN 47