Hi all,
Several stations have made the point that the plots produced by Brian,
Steve, and Dex are not a true reading of conditions. This is partially true
as outlined in my previous diatribes. Rik organised a mass plot of CFH back
in Dec 2000 (or was it 1999) before it went off air. We received logs from
widely spaced European stations and they were all very different. The peaks
and troughs all appeared at different times. So on that basis "yes a beacon
only reads the path conditions between you and the beacon transmistter
site". The conditions can be different if one moved as little as 25kms away.
There is evidence from the early tests that the paths correlated very well
with CFH levels in the UK....but then our target listener VE1ZJ was only a
few miles from Newport Corner, Halifax. QRSS3 signals popped out of the
noise coincident with peaks in CFH received at my location. Remember we are
often using QRSS60 now, which I think is another 13dB "gain"
The way to use the beacons is to study the levels against a benchmark of
some kind, like my "artificial" average plots. This immediately tells
whether conditions are better of worse that the night before, or last week.
The next thing is to try to relate the conditions to the "phase" of a
geomagnetic event. I tried to indicate three distinct phases in my HFC2000
paper. One then needs geomag indexes going back about a month. These are
available as a compact text file at 3 hourly intervals from NOAA at
www.sec.noaa.gov/ftpdir/indices/old_indices
which I find most useful. You can access archive for the last ten years or
so. I use the Kp index because it is logarithmic, and so seems to give
sensible but small "warning" numbers".
Kp<3 I find it difficult to see the effects but that is not suprising
during a solar peak
Kp=4 I think we have seen a beneficial effect after a long quiet (Kp<3)
period
Kp=5 this is slated as "Minor Storm" and does depress night-time conditions
about 3 days after the storm (depending upon the lattitudes of the path)
normal length of effect up to a week.
Kp=8 Major storm, enhanced day-time skywave and very depressed night-time
levels
starting about 3 days after the event again. The effects (poor night-time
levels) can last from 2 weeks up to a month.
The most consistent conditions are during a quiet period when there has not
been a storm for several weeks and Kp is in the 1-2 range. This does not
give the best levels but there is little fading, perhaps one trough at about
0230-0300z.
Best levels seems to be achieved on the "coat-tails" of an event as the
precipitated electrons are decaying. Laurie and I have used a guide of about
14 days into an event, and this has been found retrospectively to work
reasonably well.
The problem with the last conditions is that they depend upon the
constructive interference between several propagation paths of different
lengths, so they are very dependent on the geography of the stations
involved. They can however provide enhancement of up to 10dB over "quiet"
path levels.
The situation at present is that we have had a quiet period (late Dec early
Jan) followed with some isolated Kp=4 conditions that led to spectacular
levels in the second two weeks of Jan. We then had a minor storm Kp=5 around
the 23rd Jan which killed these good times, and the conditions have been
"topped-up" by a succession of "unsettled" (Kp=4) periods which have kept
the level of precipitated electrons in the D-layer up to absorbing
densities. these Kp=4 after the strom are extending its effect whereas after
a quiet period they were giving up "highs"
Of course while these points affect the path to Laurence at Anchorage, PCAs
Stratwarms, and the auroral curtain also help to complicate the picture.
I hope that is not too confusing but it is how I see conditions developing.
The LF propagation variables are many and complex, and there is no single
"magic number" that will give "right answer". There is no doubt that the
tireless work of several stations in providing continuous monitoring of
these commercial stations gives us valuable data. I joke that in about
another 10 years time, when we have data for a whole solar cycle, we might
have some handles on it. I doubt it will be that easy!!
My invaluable "Propagation Experts tool", my Las Vegas Lucky Rabbit's paw
insists that I add a "health warning" ....he says he is doing his best. To a
certain extent it is like early weather forecasting......if you say tomorrow
will be like today, you will be correct slightly more than 50% of the time.
I am afraid my abilities at LF forecasting are about in that league. Things
change relatively slowly, so maybe its not a bad method if you dont have
anything better.
Please if you know that I am making a fool of myself, and share the
information with me. This is very much a learning exercise for me, but my
thoughts are based on lots of recorded data, not clever theories or
"computer simulations" (Oh Meow!!).
Bore over....press delete
Cheers de Alan G3NYK
[email protected]
www.alan.melia.btinternet.co.uk/index.htm#propagation
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