Ask A Scientist© Weather Archive

name         Manny H.
status       other
age          60s

Question -   Please provide me with conversion data from frost 
point to dew point up to -75C.  I would like to get a conversion formula 
or equation from frost point to dew point.  Below a freezing point of 
water, 0C, the dew point is measured with frost point.  To convert from 
frost point to dew point, what formula do you use?  If not using a 
formula, I want to know the data from 0 CA to -75 CA in interval of 5 CA.

Manny,

I do not know of an equation to convert from frost point
to dew point.  The accurate computation for dewpoint is
difficult (using ambient vapor pressure over water)
in a polynomial or series of equations.  Computation of
frost point using vapor pressure over ice (measured with
a frost point hygrometer, chilled mirror type sensor) is
more difficult and I don't even know of an equation to
do this.

The equations to perform the calculations are beyond the
scope of this web page.  I think that it would be best to
contact a professor of meteorology or researcher directly,
or the Smithsonian Meteorological Tables, to obtain the
information.

David R. Cook
Atmospheric Section
Environmental Research Division
Argonne National Laboratory
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