|
 June
7, 2000 -- Yesterday the orbiting Solar and Heliospheric
Observatory (SOHO)
recorded a powerful series of solar eruptions including a full-halo
coronal mass ejection (CME).
"The halo CME was magnificent," says Gary Heckman,
a space weather forecaster at the NOAA Space Environment Center.
"Based on [the characteristics of the eruption], this looks
like a sure bet to produce a geomagnetic storm."
The velocity of the ejected material was at least 908 km/s, says
Dr. Simon Plunkett, an operations scientist with the SOHO coronagraph
team at the Naval Research Laboratory and the Goddard Space Flight
Center. "The CME should reach Earth in a little less than
48 hours. This would put its arrival around midday on Thursday,
June 8."
Above: This frame from a 350
kb animation shows a coronal mass ejection billowing away
from the Sun on June 6, 2000. The solid-colored blue disk in
the middle is an occulting disk that blocks out the Sun's intense
light to reveal the faint corona, along with background stars
and planets. The white circle shows the true size of Sun. These
images were captured by the wide field coronagraph on board the
orbiting ESA/NASA Solar
and Heliospheric Observatory.
Coronal mass ejections can carry up to 10 billion tons
of electrified gas traveling at speeds as high as 2000 km/s.
"Halo events" are CMEs aimed toward the Earth. As they
loom larger and larger they appear to envelop the Sun, forming
a halo around our star.
They may sound menacing, but CMEs pose little danger to people
on Earth. Our planet's magnetic field serves as an effective
shield against solar wind storms. The same familiar force that
causes compass needles on Earth to point north also extends far
into space. When a CME hits the magnetosphere -- the region around
Earth controlled by its magnetic field -- most of the incoming
material is deflected away from our planet.
If a gust of solar wind is very strong -- as this one
might be -- it can compress the magnetosphere and unleash a geomagnetic
storm. In extreme cases, such storms can induce electric currents
in the Earth that interfere with electric power transmission
equipment. Satellite failures are possible, too. Geomagnetic
storms can also trigger beautiful aurorae. These "Northern
Lights" are usually seen at high latitudes, but they have
been spotted farther south than Florida during intense disturbances.
The last time this happened was April
6, 2000.
 Left: This rare red-colored aurora over North
Carolina was photographed by Chuck Adams on April 6, 2000. The
bright object near the horizon is the Moon. Also visible in the
background are the Pleiades, Taurus, and Orion. The photographer
used a Nikon FM2 camera equipped with a 28mm f/2 lens. The exposure
time was one minute on Kodak Elite 100 slide film. (Copyright
2000, Chuck Adams, all rights reserved.)
A Double Whammy
The June 6, 2000, coronal mass ejection was accompanied by two
of the most intense solar flares since a brilliant eruption in
February 2000.
"CMEs can occur without a flare," says Dr. David Hathaway,
a solar physicist at the Marshall Space Flight Center, "but
today is the more typical case where a flare is also part of
the eruption.
"Solar flares and CMEs occur whenever there's a rapid, large-scale
change in the Sun's magnetic field. The solar active region that
produced the eruptions [on June 6] had a complicated magnetic
configuration - oppositely directed magnetic fields were seen
right next to each other."
 Whenever space weather
forecasters see a complex magnetic field like the one exhibited
by sunspot group 9026 (where yesterday's eruptions occurred)
they know that solar flares are likely. In fact, the NOAA Space
Environment Center predicted a possible major flare from 9026
several days ago. The region has been producing mid-sized flares
since it rotated into view over the eastern limb of the Sun on
June 1.
 Above: This
short animation shows the first of two X-class solar flares erupting
from sunspot group 9026 at 13:36 UT on June 6, 2000. Click on
the image for a
more complete sequence. The images were recorded by SOHO's
Extreme Ultraviolet Telescope at 304 Angstroms. The full halo
CME now heading for Earth appears to be associated with a second,
more powerful flare that occurred one and a half hours later.
Animations of that flare are available from the SOHO Extreme
Ultraviolet Telescope at
195 Angstroms or as
seen through a red Hydrogen-alpha filter (Holloman AFB).
Right: This SOHO MDI
white light image of the Sun shows the location of sunspot group
9026 on June 7, 2000.
Does this spate of solar activity means that Solar Maximum has
finally arrived?
"This is an indication that solar maximum is upon us,"
says Hathaway. There is a common misconception that "Solar
Max" is a single episode of high activity. Not so, Hathaway
cautions. The solar maximum will last over an extended period
of time, perhaps as long as two years interspersed with many
powerful solar flares and CMEs.
|
Parents and Educators: Please visit
Thursday's
Classroom for lesson plans and activities related to this
story. |
Waiting and Watching
When the CME arrives, scientists aren't sure how big the geomagnetic
storm will be.
"To get an intense geomagnetic storm from a CME we believe
that two things must happen," says Dr. James Spann of the
Marshall Space Flight Center, a co-investigator on an ultraviolet
imaging camera in orbit aboard NASA's aurora-monitoring Polar
satellite. "First, the disturbance must encounter the Earth's
magnetic field directly, as opposed to a glancing blow. Second,
the magnetosphere must already have stored energy, ready to be
released in the form of aurora. If either of these two conditions
fail, we're not likely to have an intense auroral display."
 Left:
Click
on the image to see what happens when a coronal mass ejection
strikes our planet's magnetosphere.
While no one is certain what will happen on the night of June
8, this is a rare opportunity to anticipate an auroral storm
with two full days of advance warning. There's plenty of time
to set up your camera and prepare late-night observing snacks.
You may need a cup of coffee, because the best time to spot aurora
borealis is usually during the hours around local midnight (in
this case, around the 12 o'clock boundary between June 8 and
9). The Moon will be in a waxing quarter phase, sinking below
the horizon at approximately 1:30 a.m. local time on June 9.
That will afford dark skies between moonset and dawn for rural
observers at mid-latitudes. Unfortunately for sky watchers at
higher latitudes (where aurora sightings are usually best), the
extended hours of twilight just two weeks before the summer solstice
may obscure all but the most intense Northern Lights.
The Science@NASA April 6th, 2000, aurora
gallery features a selection of photos with camera settings
suitable for recording aurora borealis. More observing tips are
available at Jan Curtis's web site "Home
of the Northern Lights."
The View from Space
A fleet of NASA and NOAA satellites will be monitoring events
in space when the CME disturbance arrives tomorrow. These include
Polar,
GEOTAIL,
ACE, POES
and others.
Researchers say that the timing of this event couldn't be better
for NASA's newest space mission -- the Imager for Magnetopause
to Aurora Global Exploration (IMAGE) -- a unique satellite dedicated
to the study of space storms. IMAGE's 'first
light' pictures of electrified gas in Earth's magnetosphere
were released just this week.
 "We've
been waiting for just such an event," says NASA/Marshall's
Dr. Dennis Gallagher, a co-investigator on the IMAGE mission.
"Hopefully, IMAGE will be in the right place in its orbit
at the right time to see the start of any resulting storm in
the Earth's magnetosphere."
Right: This sequence of pictures captured by the Ultraviolet Imager on
NASA's Earth-orbiting Polar
satellite shows an auroral storm over northern Asia on February
24, 2000. Because it records ultraviolet light, Polar's UV camera
can see aurora from space on both the day and night sides of
Earth. Polar is one of several missions operating as part of
the International Solar Terrestrial Physics (ISTP)
program. ISTP and IMAGE complement and support one another.
"Before IMAGE, if we wanted to understand what happened
during a storm like the one that's coming, we had to combine
thousands of point-by-point measurements taken by different satellites
during many distinct storms," continued Gallagher. "No
single satellite had a continuous, global view of all the action.
"It would be like trying to understand the rules of major
league baseball if you were only allowed to watch a few random
moments of different games while wearing blinders that only let
you see a little bit of the field at once -- like the first base
line or right field -- but nothing else. If you watched several
different baseball fields in this way over many years, you might
eventually start to put together what baseball is all about,
but it would be very difficult. Now imagine what you can learn
about the game if you were suddenly given sight and could see
the whole field at once throughout every game.
"That's how it is with IMAGE and the magnetosphere. We can
see the whole thing at once for the first time. I hate to take
advantage of this comparison, but with IMAGE it's a whole new
ball game!"
Stay tuned to Science@NASA
for news and updates about the coming geomagnetic disturbance.
Below: Solar Flares are classified by their x-ray flux
in the 1.0 - 8.0 Angstrom band as measured by the NOAA GOES-8
satellite. On June 6, 2000, two solar flares from active region
9026 registered as powerful X-class eruptions.
SOHO is a cooperative project between the European Space
Agency (ESA) and NASA. The spacecraft was built in Europe for
ESA and equipped with instruments by teams of scientists in Europe
and the USA.
Southwest Research Institute manages the IMAGE project
and leads the IMAGE science investigation. The IMAGE Principal
Investigator is James L. Burch. |
