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Message-ID: <C25959E8060E4D32B5EFB416101CFD35@gnat>
From: "Alan Melia" <alan.melia@btinternet.com>
To: <rsgb_lf_group@blacksheep.org>
References: <D012DF010E7A46B3B14D54F1537D8A90@AGB> <4F54B686CBDD4096901F642791F2E253@gnat> <op.whlkim1fyzqh0k@pc-roelof>
Date: Tue, 17 Jul 2012 19:02:13 +0100
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Subject: LF: Re: Kyoto Dst question
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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" <roelof@ndb.demon.nl>
To: <rsgb_lf_group@blacksheep.org>
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
>