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Subject: Dewpoint


From: Walter Henry <whenry>
Date: Monday, August 26, 1991
The following discussion took place in sci.geo.meteorology and is
reposted here without the knowledge or permission of the authors.

 Article: 1019 of sci.geo.meteorology
 From: moonunit [at] meteor__wisc__edu (Chris Bovitz)
 Newsgroups: sci.geo.meteorology
 Subject: Dewpoint
 Date: 21 Aug 91

 In article <1991Aug21.095313.32841 [at] kuhub__cc__ukans__edu>
                 arritt [at] kuhub__cc__ukans__edu writes:
 >In article <1106 [at] uswnvg__UUCP>, cjackso [at] uswnvg__UUCP (
 >               Clay Jackson) writes:
 >> Does anyone have the formula for obtaining dewpoint from RH and
 >> dry bulb temp (and vice versa)?
 >The following article is very useful for this type of problem. It
 >also has formulations for the lifting condensation level, equivalent
 >potential temperature, etc., all to very high accuracy.

 Bolton, D., 1980: The computation of equivalent potential temperature.
 Monthly Weather Review, 108, 1046-1053.

 In the _Smithsonian_Meteorological_Tables_, there is a formula which
 will give you the actual vapor pressure (use dew point temp) and the
 saturation vapor pressure (use dry bulb temp).  Since RH = E / Es (where
 E = vapor pressure, Es = saturation vapor pressure), you know any two,
 you can get the third.

 If you use the Sixth Revised Edition (1951), there is an error in the
 Goff-Gratch equation's second-to-last term: it should be multiplied by


 Chris Bovitz              | Twins Update: (08/20)  beat SEA 10-5
 Department of Meteorology |     AL West:   MIN  72-49   --
 Univ of WI - Madison      |                CHI  67-53   4.5
 moonunit [at] meteor__wisc__edu  |                OAK  66-55   6

 Article: 1021 of sci.geo.meteorology
 From: 2me [at] mace__cc__purdue__edu (M Bosilovich)
 Newsgroups: sci.geo.meteorology
 Subject: Dewpoint
 Date: 21 Aug 91

 I'm rooting through my memory, but I think that the Clausius-Clapeyron
 equation is what you require. It has many forms but this should help

      ln(es/e) = L/Rv * (1/Td - 1/T)

      e/es represents the RH, Rv = 461 J/kgK,  L=2.5x10^6 J/kg.

 This is a very useful form.

 You may want to double check this with some meteorological textbook, as
 I did this note off the top of my head.

 Mike B.    2me [at] mace__cc__purdue__edu
 Purdue University  Dept. of Earth and Atmospheric Science

 Article 1050 of sci.geo.meteorology:
 From: JG68 [at] LIVERPOOL__AC__UK
 Newsgroups: sci.geo.meteorology
 Subject: Dewpoint
 Date: 23 Aug 91

 On dew point from RH and T dry

    see, Sargent, G.P. (1980). Computation of vapour pressure, dew-point
   and relative humidity from dry_ and wet_bulb temperatures,

   within certain ranges the following may be used

    Td = U(0.198 + 0.0017T) + 0.84T -19.2

   where Td is dew point temperature Celsius, T is dry bulb Celsius and U
    is relative humidity, per cent (%).

    this equation is supposed to give T dew values within 1 C of the true
     value over the temperature range 0 C to + 30 C and RH values of 100
     per cent to 40 per cent

     Hope this is of some help.

     Dr. Andy Morse,                JG68 [at] UK__AC__LIV
     Department of Geography,
     University of Liverpool,

                  Conservation DistList Instance 5:16
                  Distributed: Monday, August 26, 1991
                        Message Id: cdl-5-16-007
Received on Monday, 26 August, 1991

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