Hi Stefan, No generally a geomagnetic event is a collision with a plasma cloud.
If it "reconnects" i.e its field is southward pointing, Alarge number of hot
ions and electrons are injected into the ring current (van Allen region) these
gradually leak/diffuse into the ionosphere and have the same effect as daytime
photo-ionised electrons.....they absorb RF. They are much hotter (higher
energy....velocity) than the photo-ionised electrons so they last all night
too. the result can be an extra roughly 12db per hop (approx 2000km) So it
tends to wipe ot DX.
The good condx do not reappear when the Kp returns to normal because rge ring
current acts as a reservoir of this charge and it "leaks" into the ionosphere
at the strained/distored edge of the magnetoshere at the dawn edge. The Dst
index is a measure of the magnetic field at the equator due to this circulating
trapped charge. So the index acts like a fuel gauge indicating the quantity of
trapped charge left. rop conditions at LF will be affected until the index
rises to -20nT (nanoTeslas). this can in the event of a massive event take up
to a month though odd days toards the end of the period may be better than
others.
Short, one hop, paths will only see a slight effect. the attenuation is
cumulative every time the signal needs to execute an ionospheric "bounce". My
empirical "feel" for this is that it can be of the order of 6 to 12dB extra
attenuation per "bounce". Hence only a slight reduction of signal on the TF
grabber
The effect of signal attenuation after a mag storm is well documented in
professional papers including many by Jack Belrose VE2CV ....a giant in this
area. It was only recently with satellite measurements that the reasons began
to be understood. I caught up with this due to a contact in NASA.
It is a very complex situation, that I dont pretend to fully understand.....but
no-one has cuffed me round the ears and said "That's not how it is"......with
data to prove it....yet. So I keep sticking my neck out :-))
The thing is thanks to many of the reports and help I have had from the LF gang
.......I can say ..."it seems to work" as a hypothesis (I wouldn't dare call it
a theory)
http://www.alan.melia.btinternet.co.uk/latest.htm is I am afraid out of date at
the moment but there are lots of useful URLs
Alan G3NYK
--- On Thu, 8/3/12, Stefan Schäfer <[email protected]>
wrote:
> From: Stefan Schäfer <[email protected]>
> Subject: Re: LF: What say the Propagation Gurus?
> To: [email protected]
> Date: Thursday, 8 March, 2012, 20:26
> Hi Alan,
>
> What do you think, could the high geomag activity be an
> improvement for the parth DL-> VK/ZL? The path has a
> bearing of 79 deg from here, so maybe its good that the
> signals coming through the auroral oval are well
> attenuated.
> This is the path DK7FC -> VK1SV:
> http://no.nonsense.ee/qthmap/?qth=JN49IK&from=qf44mt
>
> 73, Stefan/DK7FC
>
> Am 07.03.2012 16:11, schrieb ALAN MELIA:
> > Sorry for letting you all down......after all those
> quiet periods just as things get interesting, I have had a
> major PC crash and have not rebuilt that machine
> yet(Idleness rules!). It has my html editor and images on
> it. I am keeping tabs on things with a notebook.
> >
> > Unfortunately I dont have all the "research" bookmarks
> on this machine. The SWPC warning email suggests a Kp of 6
> from the first storm but I believe there may be a bigger one
> on the way( arrive thursday nite or friday ). There is the
> possibility that the effects will be additive leading to a
> prolonged period of poor conditions.
> >
> > The state of the recovery is best indicated by the Dst
> index, and the rate it is returning towards -20 nT. I would
> not be surprised if conditions were down for around 3 weeks,
> with localised better days in the lst week. The consolation
> is that daytime propagation my improve for a couple of days
> after the mag storms, but it will never be better than the
> night-time conditions.
> >
> > Alan
> > G3NYK
> >
>
>
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