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wetbulb_stull

Calculate wet bulb temperature at standard sea level pressure (1013.25 hPa) using the method of R.Stull.

Available in version 6.4.0 and later.

Prototype

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

	function wetbulb_stull (
		t          : numeric,  
		rh         : numeric,  
		iounit [2] : integer,  
		opt        : logical   
	)

	return_val [dimsizes(t)] :  float or double

Arguments

t

Scalar or array containing temperature(s) [ units see iounit ].

rh

Scalar or array containing relative humidity in percent (%).

iounit

An integer array of length 2 which specifies the units of the input t and returned wetbulb temperature:

  • iounit(0)=0 input t (degC)
  • iounit(0)=1 input t (degK)
  • iounit(0)=2 input t (Farenheit)

  • iounit(1)=0 returns units degC
  • iounit(1)=1 returns units degK
  • iounit(1)=2 returns units Farenheit

opt

Currently not used. Set to False.

Return value

A scalar or an array of the same size and shape as t. The output will be double if t is of type double. The return units are specified by iounit(1).

Description

Quote from abstract: The equation was found as an empirical fit using gene-expression programming. This equation is valid for relative humidities between 5% and 99% and for air temperatures between -20C and 50C, except for situations having both low humidity and cold temperature. Over the valid range, errors in wet-bulb temperature range from -1C to 0.65C, with mean absolute error of less than 0.3.

Reference:  Stull, R., 2011: Wet-bulb temperature from relative humidity
            and air temperature, J. Appl. Meteor. Climatol.
            http://journals.ametsoc.org/doi/pdf/10.1175/JAMC-D-11-0143.1

Examples

Example 1:

   T  = 20.0            ; degC
   RH = 50.0            ; %
   TW00 = wetbulb_stull(T, RH, (/0,0/), False)
   print(TW00)

   T  = 20.0 +273.15    ; degK
   RH = 50.0
   TW10 = wetbulb_stull(T, RH, (/1,0/), False)
   print(TW10)

   T  = 1.8*20.0 + 32   ; degF
   RH = 50.0
   TW20 = wetbulb_stull(T, RH, (/2,0/), False)
   print(TW20)
The output from each each would be the same as TW00::

   Variable: TW00
   Type: float
   Total Size: 4 bytes
               1 values
   Number of Dimensions: 1
   Dimensions and sizes:	[1]
   Coordinates: 
   Number Of Attributes: 3
     long_name :	Wet Bulb Temperature via Stull
     units :	degC
     reference :	http://journals.ametsoc.org/doi/pdf/10.1175/JAMC-D-11-0143.1
   (0)	13.69934

Example 2:

Compare wetbulb_stull and wetbulb_Wrap (wetbulb). The wetbulb_stull was derived using a pressure of 1013.25 hPa.

   tc   = 20               ; C
   rh   = 50               ; %

   tk0  = 273.15           ; K
   tdc  = dewtemp_trh((t+tk0), rh) - tk0        ; C

   twb_stull = wetbulb_stull(t, rh, (/0,0/), False)   ; C

   p    = 1013.25          ; hPa
 ;;twb  = wetbulb(p, tc, tdc)
   twbW = wetbulb_Wrap(p, tc, tdc, (/0, 0, 0/), False)

   print(twb_stull)    ;  twb_stull=13.70

   print(twbW)         ;  twbW=13.75   ; twb=twbW