Date: Tue, 30 Oct 2007 11:26:54 +0000 (GMT)
From: John Pumford-Green GM4SLV <gm4slv@sighthound.demon.co.uk>
To: rsgb_lf_group@blacksheep.org
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Subject: Re: LF: Re: Visual Aurora and good condx... my take on it.
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Thanks for that Alan!

On the visual Au front. Last year wasn't too good for them but 2 or 3 
years ago there seemed to be a good number of them nicely spread over 
the mid-winter. Last night's display was the second one I've seen so far 
this winter, and it's only October. Hopefully there will be more to see.

Perhaps 6 years ago we had an excellent Au season. Sometimes the display 
was bright enough to be visible from inside the house through the 
window. One memorable night we were all at the pub (no connection to 
seeing lights in the sky) and were keeping a regular Au watch after 
several previous good displays. I went out to observe the northern sky 
and was disappointed to see nothing. Turning around to return to the 
warm bar I faced due south and saw an amazing display, red/green 
curtains shimmering, in the southern sky! We were actually looking at 
the rear end of the auroral oval as the annular ring sank further south. 
I think it was seen as far south as France that night. That night we 
kept watch from within the pub, as its picture windows face south...

Cheers,

John



On Tue, 30 Oct 2007, Alan Melia wrote:

> 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" <dave@davesergeant.com>
> To: <rsgb_lf_group@blacksheep.org>
> 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
> >
> >
> 
> 
>