2003 - Weathering Space
the past two weeks, the Sun has shown some remarkable activity.
There have been no less than 8 major ('X-class') flares, from two
large sunspot groups. The fourth of these flares, on 28 October,
was the third largest on record (X17), and the fifth on 29 October
is in the top 20 (X11). Both of these flung huge amounts of material
into space - and they were directed head-on at the Earth, causing
widespread aurorae on Wednesday and Thursday nights last week.
SOHO/LASCO (ESA & NASA)
the past few hours, the Sun has emitted three further X-class flares,
the first at around 17.25 Sunday night (X8), the second at at about
01.00 (X3) and the third at about 09. 00 (X4) on Monday morning. While
these events were not directly aimed at Earth, a radiation storm is
in progress again, with consequences as mentioned below, and the Earth
may receive a glancing blow from the plasma clouds, with possible aurorae
on 3 or 4 November.
last week's head-on large events include clouds of hot gas, or plasma
from the Sun's atmosphere. They both travelled at over 7 million km
per hour - more than 5 times faster than the normal solar wind. When
events like this reach Earth, the effects depend critically on the direction
of the magnetic field that they carry: if this is North, like the Earth's,
our magnetic shield compresses but little else happens. If the field
is South, opposite to ours, then our magnetic shield is punctured in
places by magnetic reconnection, and particles can penetrate.
particles that get inside the shield cause enhanced aurora at lower
latitudes than usual, and can also cause problems for satellites, aircraft
and ground systems. This week's events are unusual in that the major
events were separated by less than a day and a half - almost unheard
of at this declining time in the Sun's 11-year activity cycle.
scientists are studying the science behind space weather using space
missions like SOHO and Cluster. Both saw all the events. They are also
studying the processes which accelerate particles in the magnetosphere,
and the effects on technological systems such as satellites and aircraft.
They are involved in projects including Mars Express/Beagle 2 and Cassini-Huygens,
on the way to Mars and Saturn respectively, both of which have weathered
the events. The last week's events will be a challenge to understand
as the events followed so rapidly, but we have some exciting data to
try and do this.
weather has four timescales. First, the X-rays, light and radio waves
from the initial event travelling at the speed of light reach us in
8 minutes. Second, high speed protons from the most dangerous flares
like these, travelling at less than the speed of light, reach us in
20 minutes to an hour causing a 'radiation storm'. These can upset satellite
electronics, degrade solar cells and cause a hazard to humans in spacecraft
or aircraft. Third, the clouds of hot gas, called coronal mass ejections,
take up to 48 hours to reach Earth: this week's were so fast they reached
us in 20 hours. Fourth, if the field is South, particles can be let
into the magnetosphere and be accelerated to become 'killer' electrons
1-2 days after the event arrives.
the two large sunspot groups causing all this activity are about to
rotate away from our view to cause a lull in their immediate effects,
scientists will again be looking at these unusually active solar blemishes
as they come into view again in 2 weeks time, half a solar rotation
Space Plasma Physics group
Solar and Stellar Physics group
recent SOHO images
data during last week's events
General news on auroras etc: www.spaceweather.com