Satgen 421  Solar Activity by GM4IHJ    (BID SGEN421)     19 April 97

On 7th April 97 Solar monitoring stations reported a Coronal Mass
Emission event, followed by a large Flare. Almost immediately some TV
commentators suggested that there might be damage to satellites,
electric power blackouts and Auroral displays, when the emitted
material reached the earth 3 or 4 days later.

The actual monitoring station reports were quite clear. The burst from
the Sun was a strong one for this low end of the Solar 11 year cycle,
but not perhaps as strong as the events we can expect in 3 or 4 years
time when Solar activity peaks. Equally important the monitor reports
stressed caution. In that a serious disturbance at the earth would
only occur if the magnetic field polarity of the Solar emission
coupled with the magnetic field of the earth.

This latter point is very important. As with 2 permanent magnets. If
you bring them together so that the like poles face one another Eg
north to north , or, south facing south, the fields repel one another.
So when in similar circumstances the polarity of the Solar Emission
is the same as the magnetic polarity of the earth, there is inward
compression of the earths magnetic field which could put some geosats
out into the full fury of the solar storm, but there is little or no
penetration of the emission particles down through the earths magnetic
field to the earths surface. So no big auroras and hence no monsterous
currents generated in the ionosphere and therefore no massive induced
outages , of domestic and industrial power distribution systems.

By contrast if the Solar emission magnetic field polarity is opposite
to that of the earth, the result is very different. Magnetic coupling
takes place and a gap opens in the outer parts of the earths magnetic
shield. Into this gap the Solar emission streams. But it cannot
penetrate down to the equator, as some unbroken earth field lines
invariably prevent this. It can however migrate up between the field
lines and down through their open ends onto the north and the south
magnetic poles, where it causes enhanced polar zone HF propagation,
quickly followed by Aurora, and possible power outages.

In the 7th April incident there was little or no coupling with the
earths magnetic field, so no large aurora developed and no serious
power outages were reported when, the solar emmission travelling at
about 1 million miles per hour reached the Earth after travelling for
93 hours. It should be clear from this episode how important it is to
know the Solar emission magnetic polarity. The problem is the mass
relationship of the earth and the Sun, which results in the balance
point between Earth gravity and, Solar gravity being 92 million miles
from the Sun and only one million miles from the earth. This so called
Lagrangian point is the only place between earth and Sun where we can
put a solar observation satellite and have it stay there without using
massive amounts of power to maintain its station. Satellite SOHO
presently orbiting Lagrange One gave superb warning of the original
Coronal Mass Emission only 9 minutes after it occured because it has a
clear view of the Sun,. However we cannot presently be sure of the
direction of the emissions magnetic polarity until it passes SOHO just
1 hour from earth.