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wetbulb

Compute wetbulb temperature.

Available in version 6.4.0 and later.

Prototype

	function wetbulb (
		p    : numeric,  
		tc   : numeric,  
		tdc  : numeric   
	)

	return_val [dimsizes(p)] :  numeric

Arguments

p

A scalar or multi-dimensional array of pressures [hPa/mb].

tc

A scalar or multi-dimensional array of temperatures [C]. Must conform to p.

tdc

A scalar or multi-dimensional array of dew point temperatures [C]. Must conform to p.

Return value

The returned wet bulb value(s) will have the same shape and size as p. It will be type double if any of the input arguments is type double; otherwise the values will by type float.

Description

This function returns the wet-bulb temperature given the temperature [t; degC], dew point [td; degC] and pressure p [hPa]. See p.13 in Stipanuk (1973), for a description of the technique.


Source: 
   Thomas W. Schlatter and Donald V. Baker: 
   PROFS Program Office, NOAA Environmental Research Laboratories, Boulder, Colorado.

Reference:
   Stipanuk, G.S., (1973) original version.
   Algorithms for generating a skew-t, log p diagram 
             and computing selected meteorological quantities.
   Atmospheric sciences laboratory
   U.S. Army Electronics Command
   White Sands Missile Range, New Mexico 88002
   http://www.dtic.mil/dtic/tr/fulltext/u2/769739.pdf
   http://badpets.net/Documents/Atmos_Thermodynamics.pdf

f90 verion of code:
   http://www.caps.ou.edu/ARPS/arpsbrowser/arps5.2.4browser/html_code/adas/mthermo.f90.html
   http://www.caps.ou.edu/ARPS/arpsbrowser/arps5.0Beta8browser/html_code/arps/thermolib3d.f90.html

See Also

Meteorological functions

Examples

Example 1: Compute wet bulb temperature. Source Wallace & Hobbs (1977); page 106.

   p   = 1000                   ; hPa, mb    
   tc  =   15                   ; C
   tdc =    4                   ; C

   twb = wetbulb(p, tc, tdc)    ; ===> 9.3C

Example 2:  Compute wet bulb temperature.

   p   = (/1000, 975  , 850   /)                   ; hPa, mb    
   tc  = (/40  , 30   , 20   /)                    ; C
   tdc = (/27.6, 26.17, 14.37/)                    ; C

   twb = wetbulb(p, tc, tdc)

   print(sprintf("%6.1f",p)+sprintf("%6.1f",t)+sprintf("%8.2",td)+sprintf("%8.2f",twb))

The (edited) output is:

           P       T      TD     TWB
   (0)	1000.0   40.0   27.60   30.45    
   (1)	 975.0   30.0   26.17   27.20
   (2)	 850.0   20.0   14.37   16.45

Example 3

Given temperature (C), relative humidity (%) and pressure (hPa), compute wet bulb temperature. The dew point function (dewtemp_trh) requires degrees K while the wetbulb function requires degrees C. The values returned from an interactive wet bulb calculator have been added for comparison.

   p   = (/1000, 975, 850/)                  ; hPa
   tc  = (/40, 30, 20/)                      ; C
   rh  = (/50, 80, 70/)                      ; %

   tk0 = 273.15                              ; compute dew point; compute to K
   tdc = dewtemp_trh((tc+tk0), rh) - tk0   ; C->K then K->C

   twb = wetbulb(p, tc, tdc)

   print(sprintf("%6.1f", p)+ sprintf("%6.1f",tc) \
                           + sprintf("%7.2f",tdc)+sprintf("%7.0",rh) \
                           + sprintf("%8.2f",twb))

The (edited) output is:

           P       T      TD    RH    TWB     EZC
   (0)	1000.0   40.0   27.60   50   30.45   30.43    
   (1)	 975.0   30.0   26.17   80   27.20   27.11
   (2)	 850.0   20.0   14.37   70   16.45   16.27

Example 4

Let t (C), td (C) and p (hPa) be scalar or one/two/three/four-dimensional: (1), (ntim), (ntim,ncol), (ntim,nlat,mlon), (ntim,klev,nlat,mlon). Then, the following will return an array of similar dimensionality containing the wet bulb temperatures.

  twb = wetbulb(p,t,td)