Mixing Ratio -> Dewpoint

[Charles Seman]

Dear Ben,

Please find attached a GrADS script function "qvtd.gsf" which calculates
the dewpoint temperature, given values for the air pressure (Pa) and
water vapor mixing ratio (kg/kg).  "qvtd.gsf" solves Teten's formula
(see, for example:  "The Computation of Equivalent Potential
Temperature" (Bolton, 1980, MWR) and compare formula in "qvtd.gsf" to
Equation 13.1.4a, page 551 in "An Introduction to Boundary Layer
Meteorology" by Roland B. Stull (1988)).  Also attached is a GrADS
script "test_qvtd.gs" which calls "qvtd.gsf".  Here is a sample output:

ga-> test_qvtd 100000 0.02
P, QV = 100000, 0.02
Function "qvtd":
P(hPa) = 1000
QV(kg/kg) = 0.02
QV(g/kg)  = 20
Td(C) = 25.247201488183
Td(K) = 298.397201488183

I hope this helps, and please let me know if you have any questions, OK?

Thanks,
Chuck

Ben Quinn wrote:

>Hi all,
>
>Does anyone have or know where i can find a formula to convert the mixing
>ratio to a dew point figure when i have pressure and temperature to work
>with? I've gone through the archives and spent several hours going through
>Google search results but haven't had any luck so far.  Any help would be
>appreciated!
>
>

--

********************************************************************
 Charles Seman                                charles.seman at noaa.gov
 U.S. Department of Commerce / NOAA / OAR
 Geophysical Fluid Dynamics Laboratory         voice: (609) 452-6547
 201 Forrestal Road                              fax: (609) 987-5063
 Princeton, NJ  08540-6649            http://www.gfdl.noaa.gov/~cjs/
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