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Focus on solar outbursts (Forwarded)



 
 
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Old November 27th 03, 12:31 AM
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Default Focus on solar outbursts (Forwarded)

Did anyone hear about the storm last week affecting a lot of pc hard drives?



"Andrew Yee" wrote in message
...
ESA News
http://www.esa.int

19 November 2003

Focus on solar outbursts

While scientists and aurora spotters marvel at the explosions on the Sun,
everyone responsible for the hundreds of satellites that serve human

needs, from
weather observations to car navigation, wishes that these potentially

damaging
events were more predictable.

So do the astronauts aboard the International Space Station, who recently

had to
shelter from energetic particles flung out by the most powerful solar

flare ever
recorded. Now, from space observations of the Sun going back more than 20

years,
experts are beginning to make more sense of the solar outbursts.

Apparently random events turn out to be signs of the Sun's diligent
housekeeping. It keeps sweeping away, out into space, untidy magnetic

fields
created by sunspots and other contortions in its atmosphere. The climax

comes in
a busy period of spring cleaning after the count of sunspots has peaked,

every
11 years. It leaves the Sun with its main magnetic field completely

overturned,
and its north and south magnetic poles swapped around.

Great blasts of gas coming from the Sun, called coronal mass ejections,
sometimes cause magnetic mayhem in the Earth's vicinity. A report

published this
month takes stock of 7 years of observations of such events by the

ESA/NASA SOHO
spacecraft. It also compares them with the mass ejections recorded in

1979-85 by
an American satellite, P78-1. Helping the scientists to decipher the

events seen
by the spaceborne telescopes are data from ground-based instruments at

Kitt
Peak, USA, and Nobeyama, Japan.

What emerges is a systematic pattern in the outbursts. It changes during

the
sunspot cycle, as the numbers of dark sunspots seen each day on the Sun's

bright
surface first increases and then diminishes again. The mass ejections are

often
directly associated with the sunspots, which always lie in the Sun's

equatorial
belt or at mid-latitudes.

Other mass ejections occur near the Sun's poles, far away from any

sunspots.
These events are most frequent at the peak of sunspot activity, but they

can
continue for a while as the count of sunspots begins to decline. By

getting rid
of the magnetic remnants of previous activity, the high-latitude outbursts

groom
the polar magnetic fields in a new configuration.

"The Sun is like a snake that sheds its skin," comments Nat Gopalswamy of

NASA
Goddard, lead author of the new report, which appears in the Astrophysical
Journal. "In this case, it's a magnetic skin. The process is

long-drawn-out and
it's pretty violent. More than a thousand coronal mass ejections, each

carrying
billions of tonnes of gas from the polar regions, are needed to clear the

old
magnetism away. But when it's all over the Sun's magnetic stripes are

running in
the opposite direction."

A chronicle from SOHO

This report is the latest in a series of studies of coronal mass ejections

as
seen by the LASCO instrument on SOHO, undertaken recently by Gopalswamy

and his
colleagues. When SOHO began its watch early in 1996, the Sun was quiet.

There
were very few sunspots and mass ejections happened less than once a day.

But
during the most intense solar activity, 1999-2000, there were more than

five a
day, on average -- twice as many as scientists expected. What's more, the
average speed of the ejected clouds of gas doubled, from 275 to 550

kilometres
per second.

When the sunspot count passed its peak in July 2000, mass ejections

continued at
a high rate. They did not reach their own peak in frequency until October

2002.
Events followed a different timescale in the two polar regions of the Sun.

A
flurry of high-latitude mass ejections occurred near the north pole,

completing
the magnetic reversal there by November 2000. The south polar region

lagged
behind, and its new magnetic pole was not 'clean' until May 2002. In

effect, the
solar snake shed the magnetic skin first from its head and then from its

tail.

Only a minority of the coronal mass ejections have significant effects on

the
space weather near the Earth. About a hundred times a year, when the Sun

is at
its stormiest, a blast of gas aims itself directly at our planet. Because

it
appears to surround the Sun, in the SOHO images, it is called a halo

event. Its
impact on the magnetic shield that protects the Earth causes a magnetic

storm,
which can for example produce extra current flowing in power lines and

pipelines
on the ground, with the risk of causing damage to these systems and, in

extreme
cases, equipment failure.

Also potentially harmful are high-speed mass ejections occurring near the
western edge of the Sun around sunspot maximum. Although the gas does not

come
our way, energetic particles released in the outburst can do so, causing

damage
to spacecraft and endangering astronauts. Outbursts of this type are

fortunately
rare.

"The analysis of what we've recorded since 1996 takes us a big step

forward in
making sense of space weather," says Bernhard Fleck, ESA's project

scientist for
SOHO. "By clarifying when and why different kinds of coronal mass

ejections
occur, it gives us a better idea of what trouble-spots to watch, for

possible
solar outbursts, at different stages of the sunspot cycle."

Still a major challenge

For all space agencies, the Sun's outbursts pose an increasing problem. As

the
equipment of spacecraft is miniaturized, it becomes more vulnerable to

energetic
particles and electromagnetic stresses of space weather. The planning of

manned
spaceflights has to take account of the hazards to astronauts. For a

prolonged
flight, such as now contemplated for a possible manned mission to Mars,

the
calendar of likely outbursts in relation to the sunspot cycle becomes a

major
consideration.

A workshop convened earlier this month at ESTEC, ESA's science and

technology
centre at Noordwijk in the Netherlands, looked forward towards better

monitoring
and prediction services. 'Embarrassing' was the word used by Rainer

Schwenn of
Germany's Max-Planck-Institut für Aeronomie, to describe the current state

of
space weather forecasting. He pointed out that a significant number of

magnetic
storms are still not predicted ('missing alarms') and a similar percentage

of
predicted events never occur ('false alarms').

The Space Environments and Effects Analysis Section in ESTEC acts as a

focus for
Europe-wide activities. This year it has fostered, as a pilot project, a

network
of nearly 30 European space weather services, 16 of which have received
co-funding from ESA. The network will expand and more services will become
operational over the next two years. Then it will be easier to assess the

needs
and benefits, and to consider what form a long-term European space weather
programme might take.

"Until now, much of our information about space weather gained from

spacecraft
comes from missions conceived for scientific purposes," notes Alexi

Glover, who
works on the pilot project at ESTEC. "But these scientific missions have

limited
life-spans, often with no policy for maintaining the flow of data after a
mission has ended. Also, the delivery of data in near-real time is not

always
considered important for a scientific mission, whereas this would be

crucial for
any space weather monitoring mission. Meanwhile, European space weather

services
make the most of the valuable data coming from SOHO and other existing

spacecraft."

Related articles

* It's official: the biggest solar X-ray flare ever is classified as X28
http://www.esa.int/esaCP/SEM5AUWLDMD_Protecting_0.html
* Another giant solar explosion follows Tuesday's enormous solar flare
http://www.esa.int/esaCP/SEM6N9WLDMD_Protecting_0.html
* Enormous X-ray solar flare seen by SOHO
http://www.esa.int/esaCP/SEMY3X7O0MD_Protecting_0.html

Related links

* Space Weather
http://www.esa.int/spaceweather/
* ESA Space Weather Applications Pilot Project


http://www.estec.esa.nl/wmwww/wma/sp...lotproject/pil
otproject.html
* ESA space weather workshop: developing a European space weather service

network

http://www.estec.esa.nl/wmwww/wma/sp...ndex.html#agen
da
* Today's space weather
http://www.estec.esa.nl/wmwww/wma/sp..._sw/index.html
* Tomorrow's space weather forecast?


http://www.estec.esa.nl/wmwww/wma/sp...rrow_space_wea
ther.pdf
* SOHO homepage
http://sohowww.estec.esa.nl/
* SOHO overview
http://www.esa.int/export/esaSC/120373_index_0_m.html
* LASCO homepage
http://lasco-www.nrl.navy.mil/lasco.html
* Catalogue of coronal mass ejections
http://cdaw.gsfc.nasa.gov/CME_list/
* The Sun now
http://www.esa.int/export/esaCP/ASE0...tecting_0.html
* ESA Science
http://www.esa.int/science

IMAGE CAPTIONS:

[Movie 1:
http://www.esa.int/export/esaCP/SEM1...html#subhead1]
SOHO/LASCO movie of a high latitude CME in the North polar region on

February 27
2000.

Credits: SOHO/LASCO

[Image 1:
http://www.esa.int/export/esaCP/SEM1...reWeek_1.html]
Outburst of gas from near the Sun’s south pole. The bright loop is cool,
strongly magnetized material being swept away from the Sun. The white ring
inside the central mask shows the size of the visible Sun.

Credits: SOHO/LASCO

[Image 2:
http://www.esa.int/export/esaCP/SEM1...html#subhead2]
Artist's impression of SOHO spacecraft.

Credits: ESA

[Image 3:
http://www.esa.int/export/esaCP/SEM1...html#subhead3]
A blast of gas from the Sun can buffet the Earth's magnetic field.

Credits: ESA




 




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