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Hi Jim I do not know of any better predictor of the
probability of good conditions on LF than Dst. One problem is that most
things degrade the signal :-)) Also because the ionospheric return is from
around 90 to 100km altitude at night, several hops are required for completion
of the path. Fading is a big problem with the possibility that, at long
wavelengths, multipath may keep the received level depressed for long periods
even though the apparent reflection height is continually changing.
I have also seen what I have refered to as
"leakage", though I am unsure of the mechanism. After long periods of quiet
geomagnetic conditions the received signal levels are often disappointing,
despite high Dst levels >-20nT. Signals then seem to recover after a low
level geomagnetic event, around Kp=4. This low level of activity would not
normally show any effect, but after a period of depressed signal levels it will
provide a boost. I have the though that though the E-region is ionised mainly
from non-solar radiation (cosmic rays etc) and that this may not be sufficient
to retain the required refractive index over a long quiet sun period. Could this
result in leakage of some of the signal into space ? The additional
ionisation due to precipitation from the low level event boosts ionisation at
100km altitude and "plugs the gap"....repairs the leak :-) I have no hard
evidence for this other than subjective observations during quiet periods during
the solar minimum. It may be bunkum, but it works for me.
There does not seem to be a majik index that
predicts "tonight will be good", only a series of effects that can lead to
poorer conditions :-(( I guess this uncertainty is what makes LF
interesting and challenging.
Alan
G3NYK
----- Original Message -----
Sent: Monday, December 16, 2013 10:57
AM
Subject: LF: RE: Hartmut Wolff's
grabber...
Most
interesting Bob,
Considering
Dst indices and your reports for the last six weeks, is it safe to say that
-50 or greater Dst means some bad days in this band, but benign Dsts are only
a fair indicator of potentially good conditions (Dst looked good from
mid-November through 6 December, for example)? I remember some appreciated
counsel from the group in this regard, back in October. Does anyone have a
recommendation on a next-best predictive (aiding) metric for propagation
quality in this part of the spectrum? Flares? Proton flux? Preferred site for
accessing such data?
Quite
a transition (of signal strength) on Hartmut?s grabber, I?d really like to
know what might have caused that. Thanks for some really interesting data Bob,
Hartmut et al.
73,
Jim
AA5BW
Was
beginning to look like a "dead" night coming up on 73 band. Up till
0045, that is, when suddenly decodes began to appear. Starting in
transmitting WSPR 15 at 2200 this evening no decodes appeared until
0045. I went to Hartmut's grabber and the reason was obvious. A
signal emerged from nothing to what appeared to be a decodable
one. Been that way all evening with usual mild fading.
Activity on
500 also seemed to pick-up and Stefan was solid on 136 DFCW at that time
onward.
It's what I find makes these longer waves interesting, to say the
least-Bob, WG2XRS/4 [WG4XRS for short on digi modes]
NY
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