WEATHER CELLS FOUND TO FORM AROUND MAGNETIC STORMS ON SOLAR SURFACE

University of Colorado at Boulder / JILA
Note to Editors: Contents embargoed until 5 p.m. Feb. 14. Toomre will participate in a AAAS press briefing at 5 p.m. Feb. 14.

WEATHER CELLS FOUND TO FORM AROUND MAGNETIC STORMS ON SOLAR SURFACE

BOULDER, Colo., Feb. 14 -- 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 sounds 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 CU-Boulder's 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.

Internet references:

SOHO/MDI:

http://soi.stanford.edu

SOHO:

http://sohowww.nascom.nasa.gov