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September 16, 2005
SEPTEMBER’S SUN MOST ACTIVE IN 14 YEARS
A coronal mass ejection (CME) hit Earth’s magnetic field on Sept. 15, but it did not spark the strong display of auroras many people were
hoping to see. In the CME’s wake, however, a fast solar wind stream is blowing past Earth and buffeting our planet’s magnetic field. This
could cause mild geomagnetic storms. Since Sept. 7 this one sunspot (AR 798) produced nine X-class flares, the most powerful classification. In fact,
it has made September 2005 the most active month on the sun since March 1991 and the Sept. 7 record-setting X-17 flare was the fifth largest ever
observed.
With the exception of brief radio blackouts, the flares have had little effect on Earth, although the NOAA Space Environment Center warns that as
the spot continues to rotate toward Earth, agencies impacted by space weather storms may experience disruptions over the next two weeks. These
include spacecraft operators, electric power systems, high frequency communications, and low-frequency navigation systems.
This sunspot is the same one that erupted in mid-August, sparking strong auroras as far south as Utah and Colorado. Over the past two weeks, the
active region produced a series of significant solar eruptions as it made its way around the back-side of the Sun (facing away from Earth). Auroras
were spotted over the weekend in unusual places like New York, Pennsylvania, and New Hampshire.
Solar flares and coronal mass ejections (CMEs) — associated giant clouds of plasma in space — are the largest explosions in the solar
system and can pack the force of a billion megaton nuclear bombs. They are caused by the buildup and sudden release of magnetic stress in the solar
atmosphere above the giant magnetic poles we see as sunspots.
The aurora, also known as the Northern and Southern Lights, form when solar particles and magnetic fields pump energy into the Earth’s
magnetic field, accelerating electrically charged particles trapped within. The high-speed particles crash into Earth’s upper atmosphere
(ionosphere) over the polar regions, causing the atmosphere to emit a ghostly, multicolored glow.
Dramatic solar activity is getting increasingly rare as we enter into the quiet period of the Sun’s eleven-year cycle of activity. The years
2000-2001 marked the highest point of activity, but that doesn’t preclude the occasional surprise like last week’s CMEs.
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Contacts:
Rachel A. Weintraub
NASA Goddard Space Flight Center, Greenbelt, Md.
(Phone 301/286-0918)
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A view of the aurora australis (Southern lights) as taken by the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) spacecraft on Sept.
11 in ultraviolet light. Credit: NASA
View of the aurora from the ground, taken by Jeffrey R. Hapeman of Lac du Flambeau, Wis. on Sept. 2.
The LASCO instrument on Solar and Heliospheric Observatory (SOHO) eclipses the Sun to reveal a CME leaving the Sun and heading toward Earth on
Friday, Sept. 9. Credit: NASA/ESA.
A close-up of last Friday’s flare with the Transition Region and Coronal Explorer (TRACE) spacecraft. Credit: NASA/LMSAL.
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