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Re: Refraction - Corrigendum: Humidity
From: Frank Reed CT
Date: 2005 Aug 28, 06:52 EDT
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 conditions. 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. -FER 42.0N 87.7W, or 41.4N 72.1W. www.HistoricalAtlas.com/lunars