|
 July
14, 2000 -- This morning NOAA satellites and the orbiting
Solar and Heliospheric Observatory (SOHO)
recorded one of the most powerful solar flares of the current
solar cycle. Space weather forecasters had been predicting for
days that an intense flare might erupt from the large sunspot
group 9077, and today one did.
"Energetic protons from the flare arrived at Earth about
15 minutes after the eruption," says Gary Heckman, a space
weather forecaster at the NOAA Space Environment Center. "This
triggered a category S3 radiation storm."
According to NOAA space weather prediction scales, an S3 storm
can cause the following effects on satellites: single-event upsets,
noise in imaging systems, permanent damage to exposed
components/detectors,
and decrease of solar panel currents. It can also expose air
travelers at high latitudes to low levels of radiation, the equivalent
of a brief chest x-ray.
Below: This SOHO image of the July 14th
X-class solar flare was recorded by the spacecraft's Extreme-ultraviolet
Imaging Telescope at 195 angstroms. Click on the photo below for a larger
view.
A 350 kb GIF movie nicely shows the
flare, followed by a torrent
of energetic particles that arrived about 15 minutes later, creating
snow on the images as the particles bombarded the camera's electronic
detectors.
The wave of solar particles - known as a solar proton
event - is already four times more intense than any other event
detected since the launches of SOHO in 1995 and ACE in 1997.
At mid-afternoon (UT) on July 14th, the storm of particles from
the Sun was still intensifying.
(Click on photo at left for a larger
view.)
"The energetic particles
from this flare arrived very quickly," continued Heckman.
"Protons have been observed in the past to arrive between
15 minutes and several hours after a flare. This event was definitely
one of the fastest, but we don't yet have all the numbers to
say exactly how it ranks in this category."
 Soon after the solar
flare, which occurred at 1024 UT (6:24 a.m EDT), coronagraphs
on board the ESA/NASA Solar and Heliospheric Observatory recorded
a "full-halo" coronal mass ejection (CME). CMEs are
gigantic bubbles of electrified gas carrying away as much as
10 billion tons of solar material. This one appears to be heading
toward our planet at 1300 to 1800 km/s.
Right: A full halo coronal mass ejection recorded on
July 14, 2000, by SOHO's C2 coronagraph. "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.
The many speckles in the latter half of this animation are energetic
particles from a related solar flare bombarding SOHO's electronic
detectors. "The SOHO instruments look like someone aimed
a Gatling gun at them," commented NOAA's Gary Heckman.
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There's no cause for alarm. When a CME hits the magnetosphere
-- the region around Earth controlled by our planet's magnetic
field -- most of the incoming material is deflected away. If
the shock wave 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.
 "At this time, I'm making plans to look
for the aurora Saturday night," says Heckman, who lives
in Colorado.
Whether or not an auroral display is triggered by the blast depends
on the orientation of the magnetic field within the CME's approaching
shock wave. Magnetic fields with a southward directed component
can create a weak point in Earth's magnetic defenses and make
auroras more likely.
Right: 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.)
The Moon will be full this weekend when the solar disturbance
is expected to hit. Bright moonlight will outshine faint Northern
and Southern Lights, but vivid aurora could still be visible
in spite of the lunar interference. Observers across the Pacific
might be treated to the very rare sight of shimmering colorful
aurora during the
total lunar eclipse of July 16th!
 Sunspot group 9077, which triggered today's
solar flare and coronal mass ejection, exhibits a complex magnetic
field that harbors energy for powerful eruptions.
Left: This July 14th image of the Sun was captured
by the Michelson Doppler Imager
on board the Solar and Heliospheric Observatory. The large sunspot
group, numbered 9077, is near the center of the Sun's visible
disk.
"Solar flares and CMEs occur whenever there's a rapid, large-scale
change in the Sun's magnetic field," explains David Hathaway,
a solar physicist at the NASA Marshall Space Flight Center. "The
solar active region that produced the eruptions [on July 14]
had a complicated magnetic configuration. Oppositely-directed
magnetic fields were seen right next to each other."
Active region 9077 is very near the center of the Sun's visible
disk. Solar rotation will carry the sunspot group toward the
Sun's western limb by late next week. For the next few days,
however, any additional eruptions are likely to be Earth-directed.
The fireworks may not be over yet!
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 July 14, 2000, a solar flare from active region
9077 registered as a powerful X5-class eruption. Another X-class
flare from 9077 was recorded on July 12, 2000.
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. |
