THE SOCIETY FOR POPULAR ASTRONOMY
Electronic News Bulletin No. 464 2018 March 4
SUN'S MAGNETIC CAGE STOPPED SOLAR ERUPTION
NASA/Goddard Space Flight Center
New research using NASA data shows that a dramatic magnetic power struggle
at the Sun's surface lies at the heart of solar eruptions. The work high-
lights the role of the Sun's magnetic landscape, or topology, in the dev-
elopment of solar eruptions that can trigger 'space weather' events around
the Earth. The scientists examined solar flares, which are intense bursts
of radiation and light. Many strong solar flares are followed by a coronal
mass ejection, or CME, a massive, bubble-shaped eruption of solar material
and magnetic field, but some are not -- what differentiates the two
situations is not clearly understood. Using data from NASA's Solar Dynamics
Observatory, or SDO, the scientists examined a 2014 October Jupiter-sized
sunspot group, an area of complex magnetic fields, often the site of solar
activity. That was the biggest group in the past two solar cycles and a
highly active region. Though conditions seemed ripe for an eruption, the
region never produced a major CME on its journey across the Sun. It did,
however, emit a powerful X-class flare, the most intense class of flares.
What determines, the scientists wondered, whether a flare is associated
with a CME?
The team of scientists included SDO's observations of magnetic fields at the
Sun's surface in powerful models that calculated the magnetic field of the
Sun's corona, or upper atmosphere, and examined how it evolved in the time
just before the flare. The model reveals a battle between two key magnetic
structures: a twisted magnetic rope -- known to be associated with the onset
of CMEs -- and a dense cage of magnetic fields overlying the rope. The
scientists found that that magnetic cage physically prevented a CME from
erupting that day. Just hours before the flare, the sunspot's natural
rotation contorted the magnetic rope and it grew increasingly twisted and
unstable, like a tightly coiled rubber band, but the rope never erupted from
the surface: the model demonstrated that it did not have enough energy to
break through the cage. It was, however, volatile enough to lash through
part of the cage, triggering the strong solar flare. By changing the
conditions of the cage in their model, the scientists found that if the
cage had been weaker that day, a major CME would have erupted. The group is
interested in developing its model further to study how the conflict between
the magnetic cage and rope plays out in other eruptions.


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