Hi Roelof, yes if I could explain my position on this, it might help.
I noted a relationship between high geomagnetic indexes and night-time DX
signal levels on LF. The problem was that when the Kp recovered the path did
not. I hypothesised hot electron injection from the CME into the ionosphere.
However I could not believe the hot electrons could have such a long
lifetime before recombination. This was up to 4 weeks in some cases. The
effect is well reported in professional papers by Lauter and Jack Belrose
(VE2CV) in the 1960s, but no mechanism was reported that I could find.
Then a member of the VLF group Denis Gallagher who works for NASA, pointed
me at a 1992 paper. This covered the population of the equatorial ring
current from the CMEs and indicated that the ring current (the Van Allen
belt) acted as a reservoir of hot electrons (and ions). These were able to
enter the ionosphere at the sunrise edge where the magnetosphere is
distorted as it rotated towards the Sun. The depletion of the ring current
is a diffusion process, so the Dst index which is a measure of the total
charge in the Ring Current recovers slowly, a bit like a capacitor
discharge( exponentially).
I have been able to correlate poor conditions with low Dst values. Normally
0 to -20nT in quiet condx, up to -400nT at a severe geomagnetic storm
In general there is little excess night-time absorption when the Dst is
above -20nT on the Colorado University (ACE) estimate. The Kyoto figures are
not so reliable and give a value 10 to 20nT higher on average. Their figures
are estimated from ground level magnetometers corrected for their distance
from the equator. The instantaneous values can and are distorted by errors
and local aberations. This is a fact that Kyoto appreciate and corrected
values are only issued 6 months later....not a lot of use for LF propagation
prediction.:-)) The Colorado figures are estimated from measurements of the
Solar Wind by the ACE satellite, and have proved more reliable for
propagation prediction..
So yes you can get a good idea of DX propagation by monitoring Dst. remember
that a signal passes through the ionosphere every 2000km of ground range
(approximately) so a long path suffers multiple bouts of attenuation during
poor conditions. The effect on inter-EU paths is not so dramatic though it
can see 12 to 15dB reductions in signals that are only one hop away.
Sorry for the long "waffle" but I thought it might be worth airing again.
Alan
G3NYK
----- Original Message -----
From: "Roelof Bakker" <[email protected]>
To: <[email protected]>
Sent: Tuesday, July 17, 2012 4:41 PM
Subject: LF: Kyoto Dst question
Hello Alan (G3NYK),
Looking at the Kyoto website and my NAVTEX log on 518 kHz, there is
clearly a strong correlation between Dst values around 0 and good T/A
reception.
I wonder if a significant drop in the Dst value is followed by an
immediate change in propagation, or that there is some time lag?
73,
Roelof, pa0rdt
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