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satvpr_water_bolton

Estimate the saturation vapor pressure over water using Bolton's equation 10.

Available in version 6.4.0 and later.

Prototype

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_bolton (
		t          : numeric,  
		iounit [2] : integer   
	)

	return_val [dimsizes(t)] :  float or double

Arguments

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

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).

Description

Use Bolton's equation 10 to estimate saturation vapor pressure over water. The quoted accuracy is 0.3% or better for -35C < t < 35C.

 Reference:
    Bolton, David, 1980: 
    The computation of equivalent potential temperature 
    Monthly Weather Review, vol. 108, no. 7 (july),  p. 1047, eq.(10) 
    http://dx.doi.org/10.1175/1520-0493(1980)108<1046:TCOEPT>2.0.CO;2

Examples

Example 1: Show simple usage and compare with satvpr_mean_fao56 which uses slightly different empirical constants. The difference in results is small.

  t   = 15.0                         ; degC ; iounit(0)=0 , degC
                                              iounit(1)   , hPa, Pa, kPa
  esat_0  = satvpr_water_bolton(t, (/0,0/))   ; 17.04077 hPa 
  esat_1  = satvpr_water_bolton(t, (/0,1/))   ; 1704.077 Pa 
  esat_2  = satvpr_water_bolton(t, (/0,2/))   ; 1.704077 kPa
  print(esat_0)

  esat_fao56 = satvpr_mean_fao56(t, 0)     ; 1.70535 kPa

The output is: