Magnetic Storms on the Sun Have Weather Cells

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