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Office of News Services
University of Colorado-Boulder
Boulder, Colorado

Contact: 
Juri Toomre, (303) 492-7854, jtoomre{at}lcd.Colorado.edu 
Bradley Hindman, (303) 492-7806, hindman{at}lcd.Colorado.edu 
Jim Scott, (303) 492-3114

Feb. 14, 2003

Note to Editors: Contents embargoed until 5 p.m. Feb. 14.  Toomre will 
participate in a press briefing at the AAAS meeting at 5 p.m. Feb. 14.

WEATHER CELLS FOUND TO FORM AROUND MAGNETIC STORMS ON SOLAR SURFACE

Clusters of sunspots form their own weather patterns on the sun, 
according to new observations by a team of University of Colorado at 
Boulder researchers.

Professor Juri Toomre of JILA said large complexes of magnetic 
sunspots cause downdrafts in their vicinity that are fed by winds 
flowing into the sun from the surface and dissipated by strong winds 
flowing out from deep below the sunspots.

"Large magnetic complexes are the predominant source of solar flares 
and other eruptive events that can have dramatic impacts on the Earth 
and our society," said Toomre. "The surrounding wind pattern may play 
a crucial role in producing flares, and the measurement of these winds 
may prove to be a superb indicator for solar flare prediction."

The flows were discovered using sound waves detected by the Solar and 
Heliospheric Observatory, or SOHO, which can measure wind speed and 
direction over a range of depths below the solar surface. The new 
results allowed the research team to produce the first large-scale
weather maps of wind patterns in the vicinity of sunspot clusters, 
otherwise known as magnetic active regions, he said.

The results were presented at the American Association for the 
Advancement of Science annual meeting in Denver Feb. 13 to Feb. 18.

Only the largest sunspot clusters generate a cohesive outflow pattern 
deep below the sun's surface, Toomre said. These complexes can last 
for months and are vast in size. They cover a fraction of the solar 
surface roughly equal to the fraction the United States occupies on 
Earth.

The new weather maps clearly show winds near the surface that flow 
into the sunspot clusters, said Toomre, also a professor in the 
astrophysical and planetary sciences department. Stronger jet streams, 
with typical speeds of up to 100 mph, often ram into the clusters 
during periods when flare activity is high. 

The new results also reveal that active regions of all sizes on the 
sun possess surface inflows. But deep below the solar surface, strong 
outflows appear to surround only the largest active regions. Huge 
sunspot clusters also are responsible for generating the majority of
solar flares and coronal mass ejections.

"These outflows and inflows are truly fascinating," said John 
Leibacher of the National Solar Observatory in Tucson. "They suggest 
that great circulation patterns exist that have a role in holding 
these magnetic complexes together. Such flows may be key in
understanding why some complexes yield big flares." 

The winds were discovered using a technique called helioseismology, 
said Toomre. Much like ultrasound is used to produce images of a 
fetus, helioseismology uses sound waves to produce images of 
structures and flows deep within the sun. 

The primary difference is that sound waves used in helioseismology are 
generated by the sun itself. The research team created the maps from 
data produced by the Michelson Doppler Imager, or MDI, telescope 
aboard SOHO.

"We observe ripples on the surface of the sun and measure how their 
speed varies in different directions," said CU-Boulder Senior Research 
Associate Brad Hindman, a member of the JILA team. "Ripples traveling 
with the local wind move faster than ripples going against the wind, 
so we can tell the direction and speed that the material is moving."

Unlike ripples on a pond, the motions observed by MDI are caused by 
very deep solar sound waves that are about 14 octaves below the range 
of human hearing.

SOHO is a joint satellite mission between NASA and the European Space 
Agency. Headquartered at CU-Boulder, JILA is a joint institute of the 
university and the National Institute for Standards and Technology.

Illustrations of the solar research are available for downloading at:
     http://lcd-www.colorado.edu/solar-storms

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