Solar Activity Heats Up
Solar Activity Heats Up A coronal mass ejection this weekend could trigger
31, 1999: This weekend the Sun issued a reminder to anyone
who might have forgotten that solar maximum is right around the
corner. On Saturday, August 28 at 18:05 UTC, a major solar flare
erupted from a complex sunspot group crossing the sun's southern
hemisphere. The x-ray flux from the explosion registered more
than 10-4 Watts per square meter on NOAA's GOES 8 satellite,
placing the flare in the most powerful "X" category.
A somewhat weaker "M" class flare erupted from the
same sunspot group on Friday, August 27.
Right: These images captured by SOHO's LASCO C2 coronagraph show the coronal mass ejection that accompanied Saturday's solar flare. Click on the image for an even better animation.
Saturday's major solar flare was accompanied by a coronal mass ejection (CME), pictured above. The CME was not ejected directly toward Earth and most of the mass passed south of Earth's orbital plane. However, there is a chance that the outer edges of the disturbance will collide with our planet's magnetosphere around 12 UTC on August 31. There is no danger to satellites, power grids, or people, but there could be isolated episodes of intense auroral activity for 24 to 72 hours. Residents of Alaska and high northern latitudes are encouraged to watch for colorful auroral displays. The best times to observe are prior to and near local midnight, before the bright gibbous Moon rises in the east.
Left: This movie spanning 6 hours of actual time shows recent images of the Earth's auroral region taken from space by the Ultraviolet Imager (UVI) Instrument on board the POLAR spacecraft. New movies are generated every 6 hours. Hit reload for the latest animation or visit the UVI aurora home page for new pictures every 7 minutes.
The coronal mass ejection heading past Earth now is moving at about 600 km/s. That's not unusually fast as coronal mass ejections go. Previous CME's have been seen expanding away from the sun at speeds as high as 2000 km/s, and they can carry up to ten billion tons of plasma. 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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"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."
Left: A white light image of the sun from the Big Bear Solar Observatory, captured less than 2 hours before the August 28, 1999 X-class solar flare.
Space weather forecasters at NOAA's Space Environment Center have been monitoring active region 8674, which produced the latest crop of solar flares and the CME, for over a week. Since it first rotated into view, the sunspot group exhibited a complex magnetic field structure, including "delta field configurations," indicative of likely flare activity.
"Solar eruptions 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. 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.
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For more information about space weather and current solar activity, please see NOAA's Space Environment Center web site at http://www.sec.noaa.gov/.
Below: Solar x-ray emissions received by the GOES satellites indicate 3 major solar flares between August 28 and August 31, 1999. Image Credit: NOAA Space Environment Center.
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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
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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