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Feb. 5, 2002 - RELEASE NO: 02-022

SUN CRANKS OUT RARE COOKIE CUTTER FLARES

A series of rare, nearly identical solar flares with associated coronal mass ejections blasted from the Sun in November 2000. Like snowflakes, each event is believed to be unique, because flares get their energy from the destruction of magnetic fields in the Sun's atmosphere, so they can't repeat in exactly the same way. Finding a series of such similar flares is therefore highly surprising. The observation may help reveal the link between flares and certain types of coronal mass ejection, the billion-ton eruptions of electrified gas that affect Earth's space environment.

"A sequence of flare-associated coronal mass ejections (CMEs) that look and behave almost the same is interesting," said Dr. Nariaki Nitta of the Lockheed Martin Solar and Astrophysics Laboratory, Palo Alto, California, who is the lead author of a paper on this research published in Geophysical Research Letters. "It may be due to a huge, organized magnetic structure rising from within the Sun to trigger these similar great explosions, one after the other."

According to the researchers, the rising magnetic field could repeatedly rebuild a similar magnetic structure in the solar atmosphere, setting it up for carbon-copy annihilation. "It was surprising that all six short-duration flares in this sequence were associated with a CME in a similar pattern, all within 60 hours; that is, before the magnetic field could possibly recover from the previous flare/CME event in the sequence. We believe a vigorous magnetic field emergence in the active region is the key to understand this," said Nitta.

The series of solar explosions, each releasing approximately 100,000 times humanity's total annual energy consumption, was observed with the Yohkoh and the Solar and Heliospheric Observatory (SOHO) spacecraft. They occurred near the center of the solar disk, in the vicinity of a sunspot group. (Sunspots are relatively cool, dark areas on the surface of the Sun). Six flares were observed over a 60-hour period beginning at 04:50 UT on November 24. The first three in the series were similar to each other, as were the final two. The other flare, however, was less powerful than the rest, and lasted longer. The flares were similar in several ways; their shape, the way they developed over time, their ejection of high-energy particles, and their generation of high-energy light.

Each of the flares in this series was also associated with a coronal mass ejection (CME). During the period, a total of 14 CMEs were emitted from the flare region, six of which were associated with the homologous flares. Scientists are hopeful that this discovery will help them shed light on the complex relationship between flares and CMEs, both of which occasionally disrupt high-technology systems at Earth.

"Most CMEs are associated with long-duration flares, those lasting more than two hours; but all the flares in this series were short-duration, and a bunch of CMEs happened anyway," said Nitta. "This is exciting because short-duration flares may sometimes participate in the processes that launch CMEs, but we don't know how. We have much more to discover about the connection between flares and CMEs."

According to the researchers, it is difficult to determine if flares cause CMEs or vice versa, because they might be just different aspects of one phenomenon. "Early ideas about causality, one way or the other, seem to have been based upon incomplete observations. Right now we are pretty sure that flares and CMEs are inseparable physically, with some events showing more or less of the eruptive and flare-like behavior. These particular events were very impulsive and therefore help us understand these time relationships better," said co-author Dr. Hugh Hudson of the Solar Physics Research Corporation and the University of California, Berkeley.

Yohkoh is an international collaboration led by Japan, and SOHO is a mission of cooperation between the European Space Agency and NASA. Yohkoh is managed by NASA's Marshall Space Flight Center in Huntsville, Ala.

Since December 15, 2001, Yohkoh scientific operations have been suspended due to a power loss associated with an unexpected rotation in the satellite as it crossed the path of an annular eclipse over the Pacific Ocean the same day.

Yohkoh experienced an unexpected satellite-body rotation when the satellite attitude (orientation) control switched from the normal Sun-acquisition mode to the stand-by mode as the orbit crossed the annular-eclipse belt. This prevented Yohkoh's solar panels from receiving a sufficient, stable supply of sunlight.

Satellite operators have been successful at minimizing Yohkoh's power consumption by shutting down the power lines of the other instruments and heaters, and no more decrease of the battery voltage is expected at the moment. However, the satellite is still spinning, and measures to regain the normal control of Yohkoh are continuing. Many steps will be required for recharging the battery, re-establishing attitude control, and so forth. Therefore, it may take some time before scientific observations can resume.

Images, movies and links to additional information can be found at:
http://www.gsfc.nasa.gov/topstory/20011108cookieflare.html