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dewtemp_trh

Calculates the dew point temperature given temperature and relative humidity.

Prototype

	function dewtemp_trh (
		tk  : numeric,  
		rh  : numeric   
	)

	return_val [dimsizes(tk)] :  numeric

Arguments

A multi-dimensional array or scalar value equal to the temperature in K.

A multi-dimensional array or scalar value equal to the percent relative humidity. Must be the same size as tk

Return value

An array of the same size as tk.

Description

Calculates the dew point temperature given temperature and relative humidity using the equations from John Dutton's "Ceaseless Wind" (pp 273-274). Missing values are ignored.

Note: If you input a value of RH < 0.0, then this function will return NaNs (not-a-number). This behavior was fixed in version 6.3.0.

Examples

Example 1

Wallace and Hobbs [Atmospheric Science: An introductory Survey, Academic Press, p74] state that at t=18 [C] and rh=46.5 %, the dew point temperature is approximately 6.4 C:

  tk =   18. + 273.15   ; K
  rh =   46.5           ; %

  td = dewtemp_trh(tk,rh) - 273.15  ; td = 6.3 C

Example 2

Consider a sounding with the following values:

  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 /)   

  rh =(/  75.0, \         ;  %   
          60.0, 61.1, 76.7, 90.5, 89.8, 78.3, 76.5, 46.0, 55.0, \
          63.8,53.2,42.9, 41.7, 51.0, 70.6, 50.0, 50.0 /)

  tk   = t + 273.15                ; C ==> Kelvin
  tdk  = dewtemp_trh(tk,rh)    ; dew pt temperature [K]
  tdc  = tdk-273.15              ; [C]
  tdc@units = "C"                ; add "units" attribute

Example 3

Let t and rh be four-dimensional of size (ntim,nlvl,nlat,nlon):

  td = dewtemp_trh(t,rh)  ; td(ntim,nlvl,nlat,nlon)

Example 4

Let t be four-dimensional of size (ntim,nlvl,nlat,nlon). Let rh be a one-dimensional of size (nlvl) in units of percent. Use conform to expand rh to the same size as t: