Solar Deja Vu
Solar Déjà Vu SOHO records a dazzling series of rapid-fire coronal
mass ejections on the Sun
15, 1999: When Yogi Berra made his famous remark about "déjà
vu all over again," he probably didn't have solar eruptions
in mind. But this week solar physicists did a double take, and
then a triple take, as the sun produced a rapid-fire series of
coronal mass ejections. Even Yogi would have been impressed.
Right: These images captured by SOHO's LASCO C2 coronagraph on Tuesday, October 12 show two beautiful coronal mass ejections erupting from the east (left) limb of the sun. In a more detailed animation a smaller CME can be seen on the west (right) limb occurring about midway in time between the two larger ones.
Late on Tuesday, October 12, the space-based Solar and Heliospheric Observatory (SOHO) photographed two dramatic coronal mass ejections (CMEs) in a 8 hour period. Just 6 hours later, on October 13, the spacecraft's coronagraph captured another dazzling CME. Coronal mass ejections can carry up to 10 billion tons of plasma traveling at speeds as high as 2000 km/s. When CME's collide directly with Earth they can excite geomagnetic storms, which have been linked to satellite communication failures. In extreme cases, such storms can induce electric currents in the Earth and oceans that can interfere with or even damage electric power transmission equipment.
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"Without SOHO we might not have seen these at all," says David Hathaway, a solar physicist at the NASA/Marshall Space Flight Center. "The coronagraphs on SOHO are simply indispensable for monitoring this kind of activity. None of these CMEs are headed our way, but they sure are pretty!"
SOHO (the Solar and Heliospheric Observatory) is a mission of international cooperation between NASA and the European Space Agency.
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"During solar maximum we often have more than one coronal mass ejection every day," continued Hathaway. "The basic cause of CME's is fairly well understood. Like solar flares, they occur whenever there's a rapid, large-scale change in the sun's magnetic field. Solar flares and CME's often occur together, as they did this weekend, but not necessarily because the flare triggers the CME or vice versa. One can happen without the other and frequently during solar maximum we see CME's without an associated flare."
Left: Another dazzling CME captured by SOHO on Oct 13, 1999
"Although we understand the basics of why CME's happen," he continued, "the details are still unclear. What makes the fields unstable? How rapid is the onset of the explosion? What's the detailed relationship between flares and CME's? All these questions are being actively researched, and we still can't predict CME events with any reasonable degree of accuracy."
Space weather forecasters at NOAA's Space Environment Center are currently monitoring active region 8731, a sunspot group exhibiting a complex "beta-gamma" magnetic field structure. A significant 'X-class' flare recorded at 9:01 UT on October 14 was associated with this region. (X-class flares are significant eruptions that register an x-ray flux in the 1 to 8 Angstrom band exceeding 10-4 Watts per square meter on NOAA's GOES 8 satellite.) The flare was accompanied by yet another CME shown in the animation below. Unlike the others seen earlier this week, this CME is Earth-directed. According to the Solar-Terrestrial Dispatch and NOAA's Space Environment Center the velocity of the ejected mass was approximately 700 kilometers per second near the Sun. The speed of the shock front will gradually decrease as the disturbance travels through interplanetary space. By the time it reaches Earth, the disturbance is expected to be weak compared to the background solar wind. It should produce few if any observable effects.
Below: This animation from SOHO's Extreme Ultraviolet Imaging Telescope shows the progress of a flare that erupted at 901 UT on October 14, 1999. An earth-directed coronal mass ejection can also be seen.
"Solar eruptions like these are clearly associated with sheared and twisted magnetic fields," continued Hathaway. "Whenever we see a 'delta configuration' -- that is, a sunspot where opposite magnetic poles are contained within the same penumbra -- it means something's probably about to go haywire. Beta-gamma configurations are not as complicated as deltas, but they are still complex. The trick to predicting the explosion lies in being able to look at the detailed geometry of the field around the sunspot group. Eventually, the experimental solar vector magnetograph facility here at Marshall and the vector magnetograph to be launched on the Solar-B mission may prove very useful for forecasting big eruptions.
With solar maximum just around the corner -- Hathaway and colleagues predict it will occur in mid-2000 -- solar observers should have plenty of opportunity to study solar flares and CME's, and to hone their forecasting skills.
For more information about space weather and current solar activity, including official alerts, warnings, and forecasts, please see NOAA's Space Environment Center web site at http://www.sec.noaa.gov/.
SOHO (the Solar and Heliospheric Observatory) is a mission of international cooperation between NASA and the European Space Agency. It is managed by the Goddard Space Flight Center for the NASA HQ office of Space Science.
Below: Solar x-ray emissions received by the GOES satellites indicate an X-class solar flare on October 14, 1999. Image Credit: NOAA Space Environment Center.
Solar Cycle Update October 14, 1999. Updated predictions from NASA scientists place the solar maximum in mid-2000.
Our Sun's Sizzling Corona September 2, 1999. Something funny's going on in our Sun's outer atmosphere. Read all about the mystery that made scientists flock to the path of totality for the August 11, 1999 solar eclipse.
Seasons of the Sun July 22, 1999. Predicting solar activity is a bit like forecasting the weather here on Earth. It's tricky! Nevertheless, NASA scientists have developed methods to predict the time and date of the next solar maximum.
Surfing Magnetic Waves in the Solar Atmosphere July 8, 1999. How the Solar Wind Gets Up to Speed
Solar Flares Show Their True Colors June 2, 1999. New research points to a common mechanism for spectral behavior in Solar Flares
"Cool" microflares could be solar hot spots May 31, 1999. Secret of coronal heating may be multitude of tiny blasts.
Finding the smoking gun before it fires March 9, 1999. Physicists discover a new tool for predicting solar eruptions.
Recent stories on the August '99 Eclipse
Allais Experiment Update - October 12, 1999, At any given spot along its path, the Aug. 11, 1999, total eclipse offered up to 2-1/2 spectacular minutes of total lunar coverage of the sun. But for two NASA researchers, the show's not over. They're just getting started probing a 50-year-old mystery.
This Eclipse is History - August 12, 1999, A NASA scientist views the event from the foothills of Transylvania, home of ancient legends and modern science.
Decrypting the Eclipse - August 6, 1999, scientists around the world explore the possible and mysterious effect of eclipses on the motion of Foucault's pendulum.
There goes the Sun - August 5, 1999, features general information about the August 11, 1999 solar eclipse, including the effect of eclipses on the birds and the bees, and eclipses on other planets.
Audio eclipse may fill the sky - August 4, 1999 story on investigations of ionization and radio propagation in Earth's atmosphere during the eclipse
Peering through a Hole in the Sky - June 17, 1999 story on exotic gravity measurements to be carried out during the eclipse
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