As the recent appearance of the largest sunspot for 10 years shows, our
nearest star, the Sun, is prone to spells of intense, violent activity
and unexpected, dramatic change.
Since the state of the Sun is of primary importance for all the inhabitants
of our little planet, numerous spacecraft have been launched to monitor its
mood swings. Particularly significant is the European Ulysses probe, the
only spacecraft ever to fly over the solar poles. This unique orbit meant
that Ulysses could observe the Sun and its associated space weather from a
viewpoint never accessible from Earth or other space probes.
The latest results from Ulysses will be presented by Dr. Bob Forsyth
(Imperial College, London) on Wednesday 4 April during the UK Solar Physics
Meeting, part of the National Astronomy Meeting in Cambridge.
THE ODYSSEY OF ULYSSES
More than a decade after its mission began, the Ulysses spacecraft
continues to give scientists new, three dimensional, perspectives of the
Sun’s influence on its surrounding space environment (including that of the
Earth).
Ulysses’ first flight over the Sun’s poles, which took place six years ago,
allowed scientists to understand the Sun’s influence on its surroundings
while it was in its simplest, minimum activity, state.
In November 2000, Ulysses returned to examine the south pole of the Sun for
a second time. It is now heading towards the northern polar region, which
it will fly over in September.
This time around, the Sun’s activity is at its greatest and is presenting a
much more complex picture. The rate of the spectacular eruptions known as
coronal mass ejections (which cause magnetic storms at the Earth) has
dramatically increased — although Ulysses has found that there are
proportionally fewer of these in the polar regions than near the Sun’s
equator.
One of the experiments on Ulysses is a magnetometer — provided by a team
led by Imperial College, London — which measures the magnetic fields in
space. For the Imperial College team, the most intriguing feature of the
Sun at solar maximum is that the direction (polarity) of its magnetic field
reverses. This happens almost like clockwork every 11 years.
The Sun’s reversal originates in its polar regions, the most difficult to
see when looking from the Earth. The Imperial College instrument on Ulysses
is thus ideally placed to observe the effects in space of these complex
changes in the Sun’s magnetic field as they happen.
The latest data from Ulysses show that the transition from a northward
oriented magnetic field to a south oriented one is currently under way.
This switch from one direction to another takes several months and has
implications for the severity of the magnetic storms which arrive at the
Earth. Coronal mass ejections that reach the Earth with a magnetic field
opposite to that of our planet are more likely to break through Earth’s
defences and cause serious side-effects such as power surges and compass
disruption.
Once the Sun’s magnetic field has flipped completely, the next phase of
the solar activity cycle will be officially under way.
CONTACT:
Dr. Bob Forsyth,
Space & Atmospheric Physics Dept.,
Blackett Laboratory,
Prince Consort Road,
Imperial College, London
SW7 2BZ
Phone: +44 (0)207-594-7761
Fax: +44(0)207-594-7772
E-mail: r.forsyth@ic.ac.uk
FOR IMAGES AND FURTHER INFORMATION SEE:
http://www.sp.ph.ic.ac.uk/~forsyth/reversal
