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Estimate the saturation vapor pressure over water using the Stipanuk approximation.

Available in version 6.4.0 and later.


load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/contributed.ncl"  ; This library is automatically loaded
                                                             ; from NCL V6.2.0 onward.
                                                             ; No need for user to explicitly load.

	function satvpr_water_stipanuk (
		t          : numeric,  
		iounit [2] : integer   

	return_val [dimsizes(t)] :  float or double



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


An integer array of length 2 which specifies the units of the input t and returned saturation vapor pressure:

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

  • iounit(1)=0 returns units hPa
  • iounit(1)=1 returns units Pa
  • iounit(1)=2 returns units kPa

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).


Use Stipanuk's approximation to estimate saturation vapor pressure over water.

    G.S. Stipanuk     1973            original version.
    Algorithms for generating a skew-t, log p diagram and 
    computing selected meteorological quantities.
    Atmospheric Sciences Laboratory
    U.S. Army Electronics Eommand
    White Sands Missile Range, New Mexico 88002

See Also

satvpr_mean_fao56, satvpr_water_bolton


Example 1: Show simple usage and compare with satvpr_mean_fao56 and satvpr_water_bolton which use different approximations. The differences are small.

  t   = 15.0                         ; degC ; iounit(0)=0 , degC
                                              iounit(1)   , hPa, Pa, kPa
  esat_0  = satvpr_water_stipanuk(t, (/0,0/))   ; 17.0322 hPa 
  esat_1  = satvpr_water_stipanuk(t, (/0,1/))   ; 1703.22 Pa 
  esat_2  = satvpr_water_stipanuk(t, (/0,2/))   ; 1.70322 kPa

  esat_fao56    = satvpr_mean_fao56(t, 0)           ; 1.70535 kPa
  esat_bolton_2 = satvpr_water_bolton(t, (/0,2/))    ; 1.70477 kPa

The output is:

   Variable: esat_2
   Type: float
   Total Size: 4 bytes
               1 values
   Number of Dimensions: 1
   Dimensions and sizes:	[1]
   Number Of Attributes: 5
     long_name :	saturation vapor pressure over liquid water
     units :	kPa
     NCL :	satvpr_water_stipanuk

   (0)	1.70322