Satgen 480  Auroral Timing  by GM4IHJ  (BID SGEN480)      1998-06-06

Auroral disturbance of both satellite and terrestrial radio is a
common feature of operations at stations located above Magnetic
Latitude 50. On a daily basis all the LEOsats with inclinations above
65 degrees encounter the Polar Auroral oval with consequent severe
phase and amplitude scintillation , twice on every orbit. So knowing
where the Auroral oval is likely to be located ,can provide useful
warning of where to expect trouble with reception and uplink.

But plotting the auroral oval is not straight forward. In practice the
solar wind pushes the oval polewards towards the MAGNETIC POLE, on the
sunward side , and away from the pole on the night side. So the oval
can be expected to be further from the pole at night. There is however
one awkward complication. The magnetic pole is in Northern Canada some
way from the geographic location of the earths north rotation pole. So
the thrust from the solar wind is not aimed at the geo pole except
over North America. A situation which results in the following
differences twixt Europe and North America :-

Local Magnetic Time              Scotland 4W         Chicago USA 88W
Winter Local Magnetic Noon     1040ut oval at 76N   1800ut oval at 63N
Summer Local Magnetic Noon     1120ut oval at 72N   1800ut oval at 63N
Winter Local Magnetic Midnight 2320ut oval at 62N   0600ut oval at 52N
Summer Local Magnetic Midnight 2240ut oval at 62.5N 0600ut oval at 52N
  ( all latitudes quoted in this table are geograhic latitudes )

The difference consequent on the offset of the magnetic pole is
clearly evident in the above table , and it is further complicated by
the variation in apparent solar orbit above latitude 23.5N in summer
and latitude 23.5S in winter. A situation which affects European
timings more than American ones. 

So when the radio aurora is active, each ground stations daily oval
location timings are locked to its own local magnetic time, resulting
in quite different patterns for different parts of the world. In
Europe, increases in auroral activity usually peak about 1800 local ,
ie earlier than local peak times in America. In a similar way passage
of the Harang discontinuity ( the change in direction/polarity of the
auroral arcs circulating current) which puts a break between first and
possible second (post magnetic midnight ) phases of aurora, have
different timings in Europe compared with those in America.

Extra Note - METEOR WEFAX. Activity on Meteor 3-5 LEO wefax seems to
have ceased. In its place there is a transmission on a somewhat
different orbit which is coming from Meteor 2-21 or a satellite on a
very similar orbit. The signals are not as good as those from Meteor
3-5 , being very noisy , but the in range northern hemisphere passes
have much better solar illumination than those recently experienced by
Meteor 3-5 users.