Hi Larry, well I am not sure that the professionals know a awful lot about
'em. As I understand it a CME is erupted from the surface roughly radially
as far as the main energy is concerned. I suspect it is a little like the
stone-in-the-pond and think there may be some spreading of the energy as the
cme travels. Thus I think the professionals judge whether a CME is going to
make an impact with the Earth's magnetosphere by finding where on the solar
surface it is generated. Thus if near the solar equator and in the middle of
the disc, we are certainly going to get the particles. If however it is
generated off towards the limb, then the main direction will be not pointing
at Earth so we do not get the effect.
There is another problem however, the ejected plasma mass carries a
substantial magnetic field, and the magnitude of the effect on us depends on
the orientation of that field with respect to the Earth's magnetic field.
One direction and it passes harmlessly round the earth magnetosphere, the
other direction and it couples with the Earth's field and then particle
injection is possible. I am not sure at what stage the solar observers are
able to determine this. I believe it is this effect that means that some
supposedly big CMEs seem to have little effect on us, while a smaller one
(with the appropriate orientation) will sometimes produce big auroral
So, in my experience, spotting the CMEs is only part of the story. So far I
have tried using the Kp index to see whether there will be (or maybe 'has
been') particle injection. I also believe the Kp index may be a measure of
the particle energy (...current >> Field??)...related to the field (but I
maybe wrong!).... BIG CMEs seem give a high Kp. The point is that it doesnt
immediately correlate with radio effects as it takes the particles a while
to work their way down from the poles to lower latitudes, and diffuse down
into the ionsphere.
I reckon at least 24 hours and maybe longer before the effect is felt in
radio terms. By then the Kp has usually dropped right back to quiet levels
I may be talking a load of bilge but that the best I can do from my
observations.....hope it maybe of some help....I am still trying to work up
some correlation attempts.
If anyone knows better please help me correct my naive ideas.
Cheers de Alan G3NYK
Then there are coronal hole events that happen all the time without spots,
and seem to emanate from the equatorial region of the sun.....