Satgen265   A Very Massive Aurora    by GM4IHJ               23rd April 94
BID of this msg is SGEN265  Please use this BID if you retransmit this msg

At about 0600ut on Sunday April 17th 94, GM4IHJ switched on his station
and went off to prepare breakfast , only to turn straight around as he
realised that his 50MHz Rx on Shetland Beacon GB3LER was putting out a
massive auroral signal. An aurora at this time of day was unheard of.
Indeed 20 years of operating from this station had never produced one
before . So this had to be something special, and a quick listen confirmed
that most of the 50 and 144 beacons were active. So a very big magnetic
storm had to be in progress. Big enough to push the auroral oval edge down
from its usual morning spot over Greenland, to a position where it was
just north of the Shetland Islands and extending upwards to unusually high
altitude giving back scatter propagation over all UK and into Europe, with
G0DJA and DK2ZF being the best signals on 50 and, GW0PZT being a good
signal on 144. So what caused this perhaps once in 5 or 10 years event and
how did it affect the AMSATs and the HF bands?
The event started on the Sun on 14th April, when the Japanese X ray sat
Yohkoh reported a big Coronal Mass Ejection. Material thrown out in this
event reached Earth space late on 16th April and a major magnetic storm
began to build up reaching its climax between 0600 and 0850ut on 17th
April. Back scattered European signals were S9 into Scotland at this time
but they faded very quickly around 0850 ut perhaps as earth spin moved the
UK eastwards away from the edge of the auroral oval.
There was plenty of time to examine satellite signals. Usually during
weaker Kp3 Coronal Hole induced auroras there is plenty of trans auroral
sub horizon reception of HF satellites, but none was found during this
more massive Kp9 aurora, perhaps because the auroral front extended too
high and was too near UK to be effective in the trans auroral mode. By
contrast those VHF satellites which came above the UK horizon had
dreadfully mangled signals some of which were duplicated/doubled tunable
at two frequencies. So this monster aurora did not help UK satellite
users, and it did not help HF users either. HF propagation conditions were
very poor as expected in magnetically disturbed conditions and there was
only very weak evidence of propagation of HF terrestrial beacon via the
trans auroral mode.
Things seem to have been much better in Australia where it was an evening
rather than a morning event. Indeed some good back scatter DX was reported
by southern stations , and reports of auroral DX TV suggest stations as
low in latitude as 30S were "seeing " and scattering from the aurora.
Unfortunately there have been no reports of Southern Hemisphere satellite
activity during this event. This is sad. Antipodeal stations were very
favourably placed to observe trans auroral sub horizon detections of RS
sat beacons . Any increase in sat listener/user activity in the Southern
Hemisphere in this type of event would provide a very useful check against
the mass of Northern Hemisphere information which exists. All comers will
be welcome. Anyone requiring further details should packet GM4IHJ or Trace
Ward ZL2BS @ ZL2AB.#46.NZL.OC

Remember -  northern temperate zone sporadic E will start up in the next
few weeks , climaxing in June /July . Spe can interfere badly with uplinks
and downlinks on VHF and UHF during daylight hours , and it is also a
nuisance to EME stations - More on this next week. 73 de GM4IHJ @ GB7SAN