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
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