Hi Bob --
Thanks for your quick response. Some follow up thoughts...
Some work (along with a lot of mathematical analysis) on low geomagnetic
latitude magnetospheric ducts carrying LF, MF, and even low HF signals was
done in the Soviet Union. The analysts pointed out that satellite detectors
wouldn't work very well. By the time a signal was introduced into a
magnetospheric duct, propagated, and returned, the satellite would have
moved far enough to be unable to detect the echo. There is quite a bit of
focusing at the entry/exit and the borders of a segment carrying any
particular wave are just a few hundred meters wide at 1500km above the
surface. A good analogy a flashlight beam down a bunch of parallel optical
fibers. If the satellite only tickles one fiber (aka duct) with a signal,
the satellite won't be listening to the same duct when the echo comes back.
That said, I'm not necessarily advocating magnetospheric ducting as "the
answer" for the XZ0A-USA 99 Dec path. It's a physical possibility that
should be considered, along with blobs and plumes moving across the polar
caps (a more conventional mechanism) and what you've published in "QEX".
The theorists can dredge up the possibilities... and then we must figure out
what kind of tests would discriminate between them, if we want to convert
hypothesis to theory: the fun part!
Personally, I'm curious as to how things work mostly because that makes
operating time more productive.
And, as Tom W8JI pointed out in a separate message, combinations of modes
should not be neglected. A "single right answer" often doesn't ocurr. The
explanation for a given opening is likely to involve many shifting factors.
-- Eric K3NA
--
FAQ on WWW: http://www.contesting.com/FAQ/topband
Submissions: topband@contesting.com
Administrative requests: topband-REQUEST@contesting.com
Problems: owner-topband@contesting.com
|