[50mhz] E skip question

Tue Mar 28 12:59:59 EST 2006

My favorite subject -- sporadic-E.  :-)

The idea of a causative relationship between sporadic-E ionization and
terrestrial electrical storms has recently raised its head again in the
Winter 2006 issue of CQ VHF, where ZL3NE has published a lengthy article on
VHF propagation prediction. While he seems to have documented an extensive
set of correlations between specific weather phenomena and VHF tropospheric
propagation, his proposed link between weather phenomena and sporadic-E is
described in rather sketchy terms. In my opinion, asserting the factuality
of such a link is scientifically questionable.

The hypothesis, previously proposed by others, is based on the idea that
lightning "sprites", "jets", and/or "elves" -- upward-streaming discharges
that extend from the tropospheric electrical storm through the stratosphere
and up as far as the base of the ionosphere (100 km or so up) -- are
responsible for sporadic-E ionization. (Google ["lightning sprites" AND
"sporadic-E"] for many applicable papers.) While definitely arguable, this
model is purely hypothetical, with only anecdotal evidence to back it up -- 
and the anecdotal evidence is spotty at best. The truth is, no one really
knows exactly what causes non-auroral sporadic-E ionization in most cases.
There are numerous hypotheses, but not enough hard experimental and
observational evidence to formulate a cogent theory. Many serious
investigators believe there may well be a multiplicity of phenomena that
cause ionization at this level, with complex interactions that are simply
not yet understood. The same questions first raised over 50 years ago, when
sporadic-E radio propagation was discovered, remain today:

Why does sporadic-E happen predictbly in the summer and the winter -- but
rarely in the spring and fall? Why is the winter season typically weaker,
with fewer paths open for shorter periods than during the summer? Why do the
winter openings usually occur in the evening, when summer openings occur as
frequently during the morning hours as in the evening? Why are mid-day and
early afternoon openings so much less common during either season? Why does
sporadic-E seem most prevalent in the lower to mid-latitudes in the western
hemisphere, but in the upper latitudes in the eastern hemisphere? Why are
propagation paths within the equatorial zone so rare? How can sporadic-E
beyond the geometrical single-hop limit (about 1400 miles) occur when there
is no evidence of multiple-hop propagation? Is there really an inverse
correlation between the solar cycle and sporadic-E -- i.e., stronger
sporadic-E seasons during solar cycle minima -- as some hams have suggested?
If so, why? There is simply no integrated model of sporadic-E that answers
all these questions.

For what it's worth, I think the notion of the orientation and placement of
the earth's magnetic field playing a role, as John NEØP suggests, might have
some merit. The magnetic pole is unstable, and the speed of its meandering
through the arctic region has increased sharply in recent years. Many
scientists believe we are now on the cusp of another planetary polarity
reversal, something that is known to have occurred at least 170 times in the
earth's past. Geological evidence suggests that when such shifts occur, they
are preceded by decades or centuries of increasingly unstable and ambiguous
magnetic polarity before the shift is finally complete. Evidence suggests
that we might be in such a period of increasing magnetic ambiguity now. (See
http://www.pbs.org/wgbh/nova/magnetic/ and linked sites, especially
http://www.psc.edu/science/Glatzmaier/glatzmaier.html.)

If there is a relationship between the magnetosphere and sporadic-E
ionization, and a polarity reversal is now under way, we might be in for
some changes -- but I wouldn't even hazard to guess what those changes might
look like!

Here's hoping for a terrific summer sporadic-E season this year. About six
weeks to go before we can expect things to start to happen...

Bill W5WVO

Peter Markavage wrote:
> Some believe that Sporadic E ionization can be generated by electrical
> storms, electrical disturbances in the E layer due to very fast
> movement of air, cloud to cloud ionizations due to electrical storms;
> all which can move along the jet stream. So maybe, the next time
> there is a Sporadic E opening between location points a and b, one
> might want to check what storms are moving along the jet stream. I
> would suspect that Sporadic E propagation is more weather related
> than anything else.
>
> But heck, what do I know; I'm a marketing guy.
> Pete, wa2cwa
>
> On Tue, 28 Mar 2006 05:21:04 -0000 "John Geiger" <ne0p at lcisp.com>
> writes:
>> When reading the most recent World Above 50mhz Column in QST, some E
>> skip from the September VHF contest was discussed.  The big E skip
>> opening in that contest was discussed, and Gene, W3ZZ, made this
>> comment "The first thing to notice is that being farther north, the
>> openings are nowhere near as good as for the southern stations."  I
>> have also heard in mentioned before that Eskip is better further
>> south.
>>
>> Is this true?  Are Eskip conditions better in the southern US as
>> compared with further north? If so, why?  Eskip doesn't seem to be
>> related to the F layer, which is better further south.  And Europe,
>> which is further north than much of the US, seems to get much better
>> 2 meter Eskip than we do.  Does it have to do with the location of
>> the magnetic north pole?
>>
>> 73s John NE0P
>> Moderator: Ray Brown, KB0STN
> Moderator: Ray Brown, KB0STN
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