NavList:

   

Reply

On Aug 27, 2005, at 12:34 AM, Frank Reed wrote:

> 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
>
>

Frank (or should I say, Frank I :),

That's very nice evidence for the anomalous dip that George Huxtable is
so fond of mentioning, wouldn't you say?  The most convincing
demonstration I have seen at least.  I wonder how far below "ref" the
refraction at 0 degrees altitude would go.  Seven minutes above is
astounding.

Fred

   

Reply