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    Re: Refraction - Corrigendum: Humidity
    From: Frank Reed CT
    Date: 2005 Aug 28, 06:52 EDT

    Incidentally, Marcel, it turns out that ground  level humidity has an
    interesting indirect, secondary influence on refraction  that is larger than the
    direct influence on the refractive index.
    In  average conditions of good weather, temperatures near ground level tend
    to  follow the "dry adiabatic" lapse rate of 9 or 10 deg C per km up to the
    level  where the air becomes saturated (very roughly in the range from 500 to
    1500  meters in temperate climes). From that altitude, it tends to follow the
    "saturated adiabatic" lapse rate of about 6.5 to 7 deg C per km (both of these
    rates are mildly dependent on the temperature at ground level). Over deserts,
    the dry expansion, 9-10 deg C per km, can last for five kilometers up into
    the  troposphere [try a dry desert site at uwyo below to see this]. Of course,
    daily  variability will add a large component of "noise" to these average
    On a related topic... I finally found a web site I had lost.  If you want to
    look at atmosphere soundings globally, there is a very nice web  tool here:
    http://weather.uwyo.edu/upperair/sounding.html. You can analyze  different
    regions and different seasons from the South Pacific to Greenland,  from Istanbul
    to McMurdo Sound. Try "skew-t" plots (probably easiest to see  differences in
    local patterns) or "stuve" plots (linear in temperature) or the  plain "text
    list" which could easily be used as input to your  integrator.
    42.0N 87.7W, or 41.4N  72.1W.

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