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Topband: pmaps

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Subject: Topband: pmaps
From: (Carl K9LA)
Date: Sun, 30 Dec 2001 16:41:46 -0500
In my 28 December 2001 posting, I said:

 > Those pmap pictures referenced by W4ZV, et al, only
 > tell us where visible aurora is likely to occur (low energy
 > precipitating electrons).

In W4ZV's 29 December 2001 posting, Bill challenged that statement with:

 > That's not what NOAA says about the plots, Carl

and then he quoted the text at the 

Based on the actual data measured by the satellite, my statement is 
correct. The detector onboard the satellite measures precipitating 
electrons with energies between 50eV to 20KeV. Electrons in this energy 
range get down to about 200km and 95km, respectively, and are the 
electrons that cause visible aurora. This was the intent of the 
satellite - to measure the low energy electrons that make light. The 
electrons that get to the lower E region and the D region where 
nighttime and daytime absorption occurs, respectively, are not counted.

But as the text that Bill quoted says, the oval can give us a 
"best-guess" estimate of where radio propagation paths may be degraded 
because of increased absorption. That would be where the number of dots 
perpendicular to the satellite track is very high (indicating that there 
may be even higher energy electrons precipitating down to the heights 
we're interested in) and where the solid bars are longest (indicating 
possible significantly increased ionization). Where this statistically 
occurs is generally at the equatorward and poleward edges of the oval. 
The entire oval is not full of ionization that degrades our RF.

Thus the oval doesn't really tell us about the electrons that can cause 
us problems, because it is based on measurements that exclude these 
electrons. But the oval does give us a good idea of where to look.

Carl K9LA

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