Satgen263  HF Satellites and Aurora  by GM4IHJ                 9 April 94
BID of this msg is SGEN263  Please use this BID if you retransmit this msg

The last 4 months have provided a succession of superb examples of the
cause effect connections between the Sun , Magnetic storms, Aurora and the
propagation of signal to and from HF satellites RS10 29.358 and RS12
29.408 MHz. The part of the Sun which most affects us on Earth , rotates
once every 27 days. If, as on 11th Jan 94 material escaping from a Solar
Coronal Hole reaches the Earth, we get a magnetic storm which may last for
7 days until the Coronal Hole ejecta clears the Earth. Then at 27 day
intervals we saw this same coronal hole come round to face the earth again
on 6 Feb, 6 March and 2 April 94. Coronal holes do not last forever but
there is a good chance this one will produces several days more of
magnetic storms commencing 29 April 94.

In this recent sequence, each of the above dates was followed by at least
5 days of magnetic storms, and these storms produced daily visual auroral
events and radio VHF back scatter propagation events. Given that radio
back scatter is only present when the auroral plasma is above your station
horizon. Operators have to wait until about 1500 local time before Solar
Wind pressure around the Magnetic poles begins to push the discrete
elements of auroral plasma their way. Then for roughly 8 hours or so they
can expect firstly 4 or 5 hours of radio back scatter VHF propagation,
followed after a break to about 2200 local when visual auroral displays
are likely in clear skies. All this has been known to VHF ops for many
years . What is new is that we are begining to appreciate that satellite
ops have an even longer period for good sub horizon DX.

Where you can use satellites aurorally sub horizon depends on the
satellites tracks 1500 to 0200 local. The RS sat tracks shift gradually
westwards at an average of about 1.33 degrees per day. So on successive
days you can often repeat the previous days DX by using "trans auroral"
propagation, aiming your signal straight through the aurora to a satellite
on the other side of the auroral plasma as much as 20 degrees sub horizon
- a 2200 km extension on normal sat DX. Even better still, signals are
often T9 clear tone.

Naturally there is a small catch. Sub polar regions outside Europe are
sparsely populated. So while sats over Siberia and Alaska are accessible
giving communications down to W6, W7 VE8 etc and, to JA, local ops are
generally unaware of what is happening and it is often several hours past
their bed time. 

So nothing is perfect. But with 4 consecutive repeats each featuring 5
days of potential trans auroral propagation = 20 operating days, it should
have been possible for alert ops to make some fabulous DX contacts.
Will the periods 1500 to 0200 ut April 29th to May 4th produce any good
satellite trans auroral DX in either the Northern or the Southern
Hemisphere ?
73 de John GM4IHJ @ GB7SAN