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relhum_ttd

Calculates relative humidity given temperature and dew point temperature.

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 relhum_ttd (
		t    : numeric,  
		td   : numeric,  
		opt  : integer   
	)

	return_val [dimsizes(t)] :  numeric

Arguments

t

A multi-dimensional array containing the temperature (K). Array size and shape must match td.

td

A multi-dimensional array containing the dew point temperature (K). Array size and shape must match t.

opt

Set opt=0 for units of percent and 1 for units of fraction [0-1].

Return value

A multi-dimensional array of the same sizes as t. The output will be double if any of the input is double, and float otherwise.

Description

Calculates relative humidity given temperature (K) and dew point temperature (K).

The returned values are similar to the results obtained using the algorithm in:

 
Ceaseless Wind, John Dutton. McGraw-Hill, 1976. pp 273-274

See Also

relhum, relhum_ice, relhum_water, dewtemp_trh, mixhum_ptrh

Examples

Example 1

Consider a sounding with the following values:

begin
  t  =(/  29.3,  \      ; C
          28.1,23.5,20.9,18.4,15.9,13.1,10.1, 6.7, 3.1,   \
          -0.5,-4.5,-9.0,-14.8,-21.5,-29.7,-40.0,-52.4,   \
         -59.2,-66.5,-74.1,-78.5,-76.0,-71.6,-66.7,-61.3, \
         -56.3,-51.7,-50.7,-47.5 /)
  td  = (/24.4,  \      ; C
          19.6, 15.5, 16.6, 16.8, 14.2, 9.40,  6.1, -4.2, \
          -5.1, -6.5,-12.6,-19.4,-25.0, -29.0, -33.3, -46.5, -58.2 /)


  tk   = t +273.15    ; change to Kelvin
  tdk  = td+273.15

  rh   = relhum_ttd (tk, tdk, 0)
  print(t+"   "+td+"   "+rh)
end

The output would look like:

        t     td     rh %
       29.3   24.4   75.074
       28.1   19.6   60.164
       23.5   15.5   60.9728
       20.9   16.6   76.4957
       18.4   16.8   90.4179
       15.9   14.2   89.6561
       13.1    9.4   78.293
       10.1    6.1   76.2389
        6.7   -4.2   45.8646
        3.1   -5.1   54.986
       -0.5   -6.5   63.9372
       -4.5  -12.6   53.2835
       -9.0  -19.4   42.8393
      -14.8  -25.0   41.7266
      -21.5  -29.0   50.9249
      -29.7  -33.3   70.9325
      -40.0  -46.5   50.0697
      -52.4  -58.2   49.8948

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