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Re: U.S. Standard Atmosphere Supplements
From: Frank Reed CT
Date: 2005 Aug 27, 00:34 EDT
From: Frank Reed CT
Date: 2005 Aug 27, 00:34 EDT
Marcel, you wrote: "The U.S. Standard Atmosphere Supplements, 1966 (possibly also in a newer edition) includes tables of temperature, pressure, density etc. for five northern latitudes (15, 30, 45, 60, 75), for summer (July?) and winter (January?) conditions as a function of height." I think you'll find that the US Standard Atmosphere is mostly relevant to very high altitude issues like supersonic/hypersonic flight and spacecraft re-entries (and in fact if you search for this title on google image search you'll discover photos of its cover art which shows a satellite orbiting the Earth). For refraction near the horizon, you need details on the lower troposphere which is really a weather issue. And as such you can find data on it from weather resources. Today, I did a sample calculation based on today's and yesterday's weather balloon data from Chatham, Massachusetts USA. You can access plots of this data here: http://weather.unisys.com/upper_air/skew/. I converted these data into lapse rate models as follows: Mean Lrate on both days: -6.0 deg C per km from 0 to 13km, 0 above that. For August 26: Lapse Rate, Upper Limit (m) 0, 200 -6.5, 2050 -2.6, 4375 -6.7, 6625 -8, 11000 -5, 13000 0, >13000 For August 27: Lapse Rate, Upper Limit (m) 25, 200 -6.5, 2050 -5.3, 5100 -8, 8450 -7.4, 10750 -4.9, 13000 0, >13000 Next taking the profiles, I can generate the atmospheric density as a function of altitude and from that the refraction table. As usual, all of this structure has no impact above about 3 degrees of altitude. Below 3 degrees altitude, there are significant differences in refraction as follows: Alt(deg), mean ref, ref on 8/26, ref on 8/27: 0, 35.02, 42.23, 36.32 0.5, 29.07, 30.57, 29.43 1, 24.57, 25.08, 24.74 1.5, 21.11, 21.33, 21.2 2, 18.39, 18.49, 18.44 2.5, 16.21, 16.27, 16.24 3, 14.44, 14.47, 14.46 3.5, 12.99, 13.01, 13.00 4, 11.77, 11.79, 11.78 4.5, 10.75, 10.76, 10.75 5, 9.88, 9.88, 9.88 The "mean ref" column is the refraction in minutes of arc calculated from a simple constant lapse rate of -6.0 degrees from sea level up to 13km. The other columns are the calculated refraction in minutes of arc for yesterday and today based on the lapse rate profiles described above. At the time of the balloon flights (0h GMT), these refraction tables very likely would have corresponded closely to actual observations. But the real point is simply to demonstrate the sort of daily variability that we should expect and to indicate where this variability arises and the fact that we can calculate it if desired. Atmospheric refraction is no mystery, but the atmosphere is a messy place, even on a sunny day. -FER 42.0N 87.7W, or 41.4N 72.1W. www.HistoricalAtlas.com/lunars