
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" ; This library is automatically loaded ; from NCL V6.2.0 onward. ; No need for user to explicitly load. function wetbulb_stull ( t : numeric, rh : numeric, iounit [2] : integer, opt : logical ) return_val [dimsizes(t)] : float or double
Arguments
tScalar or array containing temperature(s) [ units see iounit ].
rhScalar or array containing relative humidity in percent (%).
iounitAn 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
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) 13.69934Example 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