NCL Home > Documentation > Functions > Heat stress


Compute apparent temperature.

Available in version 6.4.0 and later.


load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/heat_stress.ncl"  ; This library is automatically loaded
                                                             ; from NCL V6.5.0 onward.
                                                             ; No need for user to explicitly load.

	function heat_apptemp (
		t          : numeric,  
		vp         : numeric,  
		w10        : numeric,  
		iounit [3] : integer,  
		opt        : integer   

	return_val [dimsizes(t)] :  float or double



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


Scalar or array containing vapor pressure (Pa).


Scalar or array containing 10-meter winds (m/s).


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

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

  • iounit(1)=0 input vp (hPa)
  • iounit(1)=1 input vp (Pa)
  • iounit(1)=2 input vp (kPa)

  • iounit(2)=0 returns units degC
  • iounit(2)=1 returns units degK
  • iounit(2)=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 or rh is of type double. The units are specified by iounit(1).


Wikipedia: Apparent temperature is the general term for the perceived outdoor temperature, caused by the combined effects of air temperature, relative humidity and wind speed.

    Australian Bureau of Meteorology

    Steadman, R.G., 1994: Norms of apparent temperature
             in Australia, Aust. Met. Mag., 43, 1-16. 

    Buzan, J.R. et al (2015): 
           Implementation and comparison of a suite of heat stress metrics
              within the Community Land Model version 4.5
           Geosci. Model Dev., 8, 151-170, 2015

See Also

Heat and Stress functions


Example 1:

   t   = 30.5      ; C
   vp  = 20.0      ; Pa
   w10 = 10.0      ; m/s
   at  = heat_apptemp(t, vp, w10, (/0,1,0/), 0)
The output is:

    Variable: at
    Type: float
    Total Size: 4 bytes
                1 values
    Number of Dimensions: 1
    Dimensions and sizes:	[1]
    Number Of Attributes: 5
      long_name :	apparent temperature
      units :	degC
      reference_1 :	Steadman, R.G., 1994: Norms of apparent temperature in Australia, Aust. Met. Mag., 43, 1-16
      reference_2 :	Buzan et al (2015): eq (1)
      NCL :	heat_apptemp
    (0)	19.566