N4XX forwarded the following message from Cary Oler who runs the Solar
Terrestrial
Dispatch Topband site (http://solar.uleth.ca/solar/www/topband.html) Also be
sure
to read Cary and Ted's articles in the March and April issues of CQ. They are
excellent and explain the strange ducting and skewing we often see on Topband.
73, Bill W4ZV
To: <topband@contesting.com>
Date: Sat, 21 Mar 1998 05:57:05 -0500
From: Ted & Susan Cohen <stcohen@erols.com>
Subject: NL7Z - Longpath from NY?
To: Tippett Bill <w4zv@contesting.com>
Cc: Oler Cary <oler@solar.uleth.ca>
Regarding the comments on the unusual propagation observed on 20 March,
I have a couple of comments:
First, K1ZM did _NOT_ hear anything from his long-path. That's absolutely out
of the question. His signal would have been in daylight - and daylight
absorption is HUGE. No, let me reiterate, it is ***H U G E***. No possibility
of that.
Second, a close examination of the Alaskan signal path indicates that at the
time of the transmission, it would have passed right through the equatorward
edge of the auroral oval. For quite a large distance, his signal actually runs
parallel to the equatorward edge of the auroral oval (but inside the oval).
I've confirmed this with POLAR aurora imagery. So his signal was almost
certainly experiencing a variety of problems - sporadic-E a definite
possibility, and odd refraction from the strong electron density gradients that
can develop there. I imagine his signal almost certainly would have been
associated with severe multipathing. I'm estimating (roughly) that his signal
was probably in the influence of the auroral ionosphere for almost 1000 km.
And the equatorward edge of the auroral oval is also a very dynamic region that
can expand and contract rapidly and vary over fairly short time-scales. What
he observed doesn't come as a surprise, considering this evidence.
Lastly, a weak solar disturbance (thought to be related to a weak coronal mass
ejection) reached the Earth a few hours before the K1ZM made these
observations. Most high-latitude signals take on a substantial amount of
flutter if they spend much time in the auroral ionosphere following the arrival
of these disturbances. The disturbance wasn't very strong, but it did push the
auroral ovals southward beyond their normal resting place, which is perhaps one
reason why this seems so odd to people. K-indices didn't respond very much to
the arrival because the IMF was directed mostly northward at the beginning of
the disturbance - and in fact, they have been northward almost ever-since. But
that doesn't necessarily diminish the impact it can have on Topband
propagation, where signals are so easily refracted. It doesn't take very much
to influence them.
I hope this sheds some light on the matter.
This is just another case where people could benefit from knowing what the
space environment conditions are like. These guys really should consider
owning SWARM. Simply knowing that a disturbance arrived a few hours earlier
changes
yourntire diagnostic process.
Anyway, I hope this helps.
Regards.
-Cary Oler
Oler@Holly.CC.Uleth.CA, Oler@Uleth.CA,
Oler@Solar.Uleth.CA, or
COler@Solar.Stanford.Edu
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