This week–
Radio waves warn
of imminent storm
an approaching storm early on,
determining the direction of the
storm’s magnetic field is tricky.
“There are currently no remote
ways of measuring the magnetic
field between the sun and Earth,”
says Justin Kasper of MIT. The
field can be measured directly
when the CME sweeps past
STEREO, but by then the storm
is only about half an hour away.
So Liu and colleagues at MIT
and the University of Michigan
at Ann Arbor propose using radio
waves from distant stars and
galaxies to probe the storm. Many
of these radio sources emit
polarised radio waves, which tend
to vibrate in a certain direction.
soho/esa/nasa
“It is very important to predict
these solar storms so we have
time to shut down spacecraft
and power grids”
stephen battersby
THEY give us brilliant auroras in
skies far from the poles. But the
outbursts of ionised gas from the
sun also have a dark side. They
can destroy satellites and knock
out power grids with little
warning. Now, a technique that
uses radio waves to probe these
solar storms could give us up to
three days’ warning of the
deadliest ones headed our way.
From time to time the relatively
steady solar wind is interrupted by
a storm, which hurls billions of
tonnes of ionised gas, or plasma,
from the sun’s outer atmosphere
at speeds of millions of kilometres
an hour. Most of these coronal
mass ejections (CMEs) miss the
Earth; others are deflected by our
16 | NewScientist | 2 June 2007
When these radio waves pass
through a CME, its magnetic field
can change the direction of
polarisation, an effect called
Faraday rotation.
Astronomers can work out the
direction of the CME’s magnetic
field from the polarisation of
these radio sources. It is no easy
task because the field is twisted
up, but the researchers have
–Beautiful but deadly– worked out that by looking at
several radio sources through the
magnetic field – but some are
CME, they can calculate the
positively dangerous.
direction of its field. “With a
Sometimes the polarity of the
number of lines of sight, you can
CME’s magnetic field is such that
disentangle both the direction of
it can merge with Earth’s own
field and which way it twists,”
field, and the writhing fields can
says MIT’s John Belcher.
disrupt radio communications
While today’s radio telescopes
and bring down power grids. The
aren’t up to the job, the Mileura
CME also dumps its cargo of high- Wide-Field Array, being built in
energy particles into the upper
Australia, is designed to watch
atmosphere, creating auroras
many sources across a large area
away from the poles, but they can of the sky – perfect for the new
also damage satellites and harm
technique. It should be ready in
spacewalking astronauts. “It
time for the next peak in solar
is very important to predict
activity around 2010, when a few
these storms so that we can do
CMEs per month will head for
something to avoid the damage,” Earth. “If we can determine the
says Ying Liu of the Massachusetts magnetic field orientation from
Institute of Technology.
Faraday rotation measurements,
While NASA’s sun-watching
we will have time to shut off
STEREO spacecraft, positioned a
spacecraft and power grids to
million miles from Earth, can spot avoid damage,” says Liu. l
this week
50 years ago
Flu threat from the Far East
A major wave of influenza is
approaching. What happens next is
anybody’s guess, but many experts
are keeping their lips sealed and their
fingers crossed.
This epidemic started in Hong Kong
in mid-April. It has since reached
India, and an increasing number of
cases are being reported from Bombay
and Madras. The Philippines has
150,000 cases, and outbreaks have
now been reported in North Borneo,
Sarawak, Formosa, Cambodia, Malaya
and Indonesia. Recently a ship that
reached Rotterdam from Jakarta
reported 300 cases of influenza
during the course of the voyage. There
have also been cases among aircraft
passengers reaching Australia via
Singapore. Modern aircraft, as we are
discovering, speed the spread of oldfashioned viruses.
That’s if it is an old-fashioned virus.
It may, of course, be a new-fashioned
one. The World Health Organization
has been working with samples of
the virus, and it seems that it is a very
different strain of the influenza A-type
virus, the strain that usually causes the
major epidemics. Its rapid spread is
probably down to the fact that nobody
has acquired immunity to it yet. Virus
type A has been studied for 10 years
and there have been big changes in it
since then.
This version seems to be fairly mild
and has so far caused few deaths. But
we should not feel complacent. There
is no vaccine against this new strain
and, more pertinently, it would be
quite impossible to produce one at
such short notice.
While it seems very unlikely indeed
that we shall have anything like the
desperate pandemic caused by the
deadly influenza virus of 1918-19, we
should regard this latest outbreak as a
sign that influenza viruses can mutate
spontaneously, and, when they do,
forming a new and deadly strain, there
is very little at the present time that we
can do about it.
From The New Scientist, 6 June 1957
www.newscientist.com