Hi Dave, yes indeed.
There are two main sources of geomagnetic storm "stimulation". The first is
the well known Coronal Mass Ejections (CMEs) that emanate from the area of
sun-spots and are usually associated with flares,but can be ejected by some
non-flare proceses as well. These are common at the Solar max when the
Sun-spot count is, of course, high. The type of shock we experienced the
other day which caused the aurora and and has been happening at irregular
intervals throughout these quiet years is known as a "coronal hole event"
this is a "tear" in the solar atmosphere which results in the spin off of
coronal material (Hydrogen ions and electrons), much the same as the
background "solar wind" The presence of a coronal hole is like somone in the
garden with a hose being called from the house and swinging round drenching
everyone as the spray sweeps round. The speed of the cooronal hole flow is 2
or three times the speed of the normal solar wind so it causes a magnetic
shock to the geomagnetic field. Some of the plasma, mainly Hydrogen ions and
electrons are able to enter the earths field at the poles, spiralling down
the lines of force to create the magical auroral "curtains" described by
John.
All is not over however as the rest of the "spray" sweeps by and some is
sucked into the magnetic "tail" of the Earth's field a bit like when you
drive a hatchback with the tail-gate slightly open and the exhaust fumes
enter the car. These ions and electrons are drawn back into the Equatorial
Ring Current in the Van Allen Belt and form a reservoir of "hot" electrons
which are bled into the ionosphere at the sunrise edge where the earth's
field is distorted by the pressure of the solar wind. These diffuse down
into the D-layer are "hot" and long lived, and give the excess night-time
attenuation experienced at LF after a "magnetic storm". This even persists
for days after the Kp index has returned to normal low or quiet levels.
After severe storms the ring current can be so highly populated that LF
signals can often be depressed for 3 or 4 weeks. This generally only happens
around the Solar max. and after Kp=9 events.
Phew.....well you DID ask Dave !!
Cheers de Alan G3NYK
----- Original Message -----
From: "Dave Sergeant" <[email protected]>
To: <[email protected]>
Sent: Tuesday, October 30, 2007 7:11 AM
Subject: Re: LF: Re: Visual Aurora and good condx
> On 29 Oct 2007 at 21:46, Alan Melia wrote:
>
> > Hi John yes a Coronal hole flow shock at around 1800-2100z period
> > pushed the Kp up to 5 which is enough to give you a display up there.
> > The radio effects will probably not be felt until tomorrow night when
> > things may be down a bit. The Dst index is only down to -35nT at
> > present but it is probably still dropping. Anyone watching overnight
> > may find the pre-dawn period is not as good as it is usually.
>
> Maybe Alan can explain why we get these auroras and high K indexes at
> the sunspot minimum when the sun spot count and solar flux have been
> at rock bottom for weeks on end?
>
> Just checked, sunspot number still at 0, solar flux still at 67. A
> index (effectively yesterday's figure) for Kiel was 22 and K is
> currently 3 though has dropped from the earlier 5 figure.
>
> But why, and also why has there been an unusual sporadic E opening
> all weekend on 10m, which is most unusual in October. The guys
> playing in CQWW this weekend had a ball! I managed a QSO with C52C in
> the Gambia yesterday afternoon on 10m with my 5W.
>
> What is producing these effects. Doesn't seem to be anything to do
> with the sun as all is stonely quiet there and certainly nothing to
> produce huge auroras? Always thought solar weather was a black art
> (and in this case BLACK seems to be the key word!).
>
> By the way I gave both John GM4SLV and Ray GI3PDN calls last night
> but nil response so it looks like my qrpp ain't getting that far.
> Signals seemed nothing out of the usual, normal peaking 589 with deep
> QSB to noise level at times, I have certainly heard both John and Ray
> at better signals so not convinced aurora or not it was affecting
> 500kHz (certainly no auroral tones).
>
> Will very shortly be reconfiguring my vertical back to its Top Band
> configuration for the winter season so will be back in the spring if
> we still have NOVs.
>
> 73 Dave G3YMC
>
> http://www.davesergeant.com
>
>
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