Solar Activity Heats Up
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Solar Activity Heats Up
A coronal mass ejection this weekend could trigger
auroral displays.
August
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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For more information, please contact: Dr. John M. Horack , Director of Science Communications |
Author: Dr.
Tony Phillips Curator: Bryan Walls NASA Official: John M. Horack |