|
Hi Markus yes that puzzled me for years (having a
feel for ion/electron lifetimes it didnt seem to make sense) BUT when you
introduce a "magnetic bottle" which is filled on the impact of the CME and
dribbled into the ionoshere daily it starts to make sense (Thanks here to Denis
Gallagher on the VLF group who has a NASA email address for pointing me in the
right direction and providing a extraordinarily good review paper as a
reference.)
I think there is the possibility of "delays" but I
am finding that there do seem to be other factors. I am still puzzling over
these. A high Dst increases the probability of good conditions but doesnt
guarantee them
:-)) There is one further factor and that is
signal leakage. If the geomag conditions are very quiet for extended periods
like during the Solar min. signals seem to decrease, I have a feeling that
some of the longer lived ionisayion in the E-region may depend on the Ring
Current charge. After a long quiet period the night-time E-layer does not
"reflect" quite so well. Conditions then improve after a small event, Kp=4,
which would under normal conditions be insignificant, and produces only small
changes to the Dst.
Alan
----- Original Message -----
Sent: Wednesday, April 10, 2013 7:40
AM
Subject: Re: LF: Best results so far from
Germany to Tasmania
Alan, thanks very
much for the detailed and interesting explanations! One thing I have
always found hard to grasp was that charges can be stored up there
for as long as several days. But it seems the clue is just the
extremely low gas density, providing the ions with a long mean lifetime
between collisions and recombinations.
As you say, Loran was nonexistent anywhere
south of Saudi Arabia (at least in this century), and of course in
2010 American activity has ceased except for a few sporadic
tests. From
watching the traces I sometimes got the impression that when on
above-average propagation existed from east Asia, the maximum enhancement from
America tended to occur one or two nights later. But this was just a
subjective notion, and I should some day try to prove it
by plotting hard data on fieldstrength etc.
Best 73,
Markus
Sent: Tuesday, April 09, 2013 10:50 PM
Subject: Re: LF: Best results so far from Germany to
Tasmania
Hi Markus, it would seem that the majority of the
"hot" precipitated electrons enter the ionosphere at the dawn and dusk edges
where the magnetosphere is distorted by the solar wind pressure. I believe
they enter at high latitudes and diffuse towards the equator. So I am guessing
that if there are any gradients they are pole towards the equator. Certainly
there is evidence from Laurence and Scott VE7TIL that they see propagation
collapse almost immediately after a geomag shock. I dont have any data for
worldwide distribution. In fact the only plottable data is that for the
N.Atlantic path to CFH. The plots from Scott suggest that the decay of the
attenuation after a shock is around 5-6dB/hour . This suggests that when
the Equatorial Ring Current is exhausted the global ionosphere returns
to the simple photo-dissociation model with solar UV activation (what a load
of pretentious rot I just wrote :-)) ) I mean we get an absorbing
daylight D-region again which disappears as soon as it becomes dark. The solar
eclipse plots of a few yeas ago suggest the free daytime electrons recombine
in seconds due to the relatively high pressure 50 to 100km altitude (it would
still make you gasp a bit though :-)) ) and their relatively low energy
(just above the ionisation level)
I wonder if your Loran data would give any
information on worldwide distribution? However I believe most of the Loran
chains are in the Northern Hemisphere (not sure if there are any around
VK/ZL
The Dst is not a measure of electrons in the
D-layer, rather it is a measure of the potential gradient driving the
exchange between the Ring Current and the Ionosphere . Thus very
low Dst indicates a high potential to drive lots of excess free electrons
into the D-region. The Dst recovery as the ring is depleted is approximately
logarithmic as one would expect for a diffusion process. I did wonder whether
measurements of total electron density would give any ideas. but I could not
make any progress with that, probably because most of the electrons will be in
the higher levels of the F-layer.
Interestingly when a big storm occurs the excess
electrons have the same effect as a flare in daytime ! They enhance the
daytime signal level for one or perhaps at most two days. The are much hotter
that the flare generated electrons so the effect lasts longer but is much
weaker than the absorption effect at night.
We may get some more ideas when the data from the
latest satellite (that found the 3rd Van Allan belt) finishes surveying the
region. I have seen it suggested that there are up to 7(I think it
was) ion filled rings reaching up to nine Earth diameters
out.
Unfortunately a good Dst doesnt guarantee good
signals.....there is something else at work. It may just be multipath but
I cant get any useful data yet. Maybe I need phase data.
Best Wishes
Alan
G3NYK
----- Original Message -----
Sent: Tuesday, April 09, 2013 7:49
PM
Subject: Re: LF: Best results so far
from Germany to Tasmania
Edgar, Stefan,
this is an outstanding result! Great to
see what is possible on LF, given a good antenna, a quiet location,
and patience paired with persistence.
Did you by chance have a look at the best SNR
in the spectrum plot? The fat parts of the trace might have
been 12 or even 15 dB, in a 7.5 mHz FFT. This would put
it within easy reach of an Opera-32 correlation detection,
and possibly even close to a WSPR-15 decode.
Alan, I assume that DST would affect
attenuation globally, without preference for one direction or another. Or
could an eastern path be better during one night, versus westward
in another?
Best 73,
Markus (DF6NM)
Sent: Tuesday, April 09, 2013 2:09 PM
Subject: LF: Best results so far from Germany to
Tasmania
LF,
Last
evening there was excellent LF propagation from EU to VK. Edgar J. Twining
(SWL) was watching the LF DX window for several weeks now. The season on
that path in spring (EU) 2013 was very poor and we already thought that the
season is over. However yesterday the path was open for a exceptional long
time and the S/N was very good! Transmissions were done in DFCW-180. I've
been on air for several days now and such a result is most probably possible
for 1 time in the year or maybe 2 years.
These are the results:
My
signal: https://dl.dropbox.com/u/19882028/LF/DK7FC%20WR%20ver%20spectrum%20-18.PNG
DCF39:
https://dl.dropbox.com/u/19882028/LF/DCF39%20WR%20ver%20spectrum%20-14.PNG
DCF39
plot: https://dl.dropbox.com/u/19882028/LF/DCF39%20WR%20ver%20plot%202013-04-08%2021-30.jpg
The
path is 16806 km, http://no.nonsense.ee/qthmap/?qth=QE37PD&from=jn49ik00wd
It
shows once again that it is always worth to transmit and to receive/watch
for exceptional conds(x) on the bands!
Many thanks to Edgar for his
continuous patience and interest to receive on 137 kHz from the other side
of the world!
73,
Stefan/DK7FC
| 
