Hi Jay,
Yes, the sferic propagation on VLF is affected as well. I can see quite
low noise background levels arround the dreamers band. This may even be
an advantage for the VLF experiments since we can do it via the
groundwave up to some 1000 km. :-)
73, Stefan/DK7FC
Am 09.03.2012 13:42, schrieb [email protected]:
Alan
Thanks for the update and insight.
Absolutely no trace of Stefan's signal in CT last night. A few nights
back he was 25+ dB s/n (in 28 mHz). Long distance VLF signal levels
below normal as well.
Jay W1VD WD2XNS WE2XGR/2
----- Original Message ----- From: "ALAN MELIA"
<[email protected]>
To: <[email protected]>
Sent: Friday, March 09, 2012 5:57 AM
Subject: Re: LF: Big solar flare - major geomagnetic storms to follow
Hi all more geomag storming this morning. It looks as though I might
have got my timing wrong. However the 56 hours to the Kp=7 event is a
bit slow for such a big event, and the predicted speed of that CME.
I suspect this mornings event may be what I refered to yesterday as a
"sub-storm". This occurs when the plasma cloud sweeps past Earth and
some is then trapped in a "magnetic bottle" in the tail of the
magnetosphere. The magnetic field becomes highly distorted and twisted
by the extra hot charge. Just as in the Sun-spots this strain is
relieved as the field snaps back into a lower energy state. The excess
energy which is released as the field collapses is transfered to the
plasma "glob". The result is that two parts of the plasma are fired
off at very high speed. one towads Earth and one away from Earth (to
conserve momentum....a basic law of physics). This mornings event was
the shock of that plasma "bullet" arriving. I believe this mornings
event may have been of this nature.
How does it affect LF? The charge from the "bullet" is injected into
the ring current so tops up the charge reservoir, and this lengthens
the period of excess attenuation in the night-time D-layer. There is
some discrepancy between the Dst estimates. The Colorado estimate is
running at about -50nT whilst the Kyoto value is around -150nT. Kyoto
is based on a number of ground located magnetometer observations and
is prone to rather wild fluctuations, and often "overshoots". The
Colorado plot is based on a calculation using the solar wind
parameters as observed by the ACE satellite. From my experience I find
the latter to be more useful/meaningful in terms of LF effects.
Overall I think this indicates a mild effect. Long distance night-time
paths will be affected for a week or so. For a good indication of the
progress of of the recovery, watch the Dst as it returns to around
-20nT....the indication of quiet, good propagation conditions. Just
before the conditions settle there can be some exceptionally good
nights, probably caused by favourable fading/multipath. These are very
location dependent and do not work for everyone.
However keep watching..... NOAA predict the possibility of more
X-Class flares from the current spots, with the associated CMEs.
Good LF DXing !!
Alan
G3NYK
|
