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A huge sunspot as big as the surface area of thirteen
Earths is growing on the Sun and has now rotated with the Sun
to face the Earth. The sunspot, in the region designated AR
9393, is the largest of the current solar cycle, making it the
biggest to appear in ten years. This region also has been a
prolific generator of stormy solar activity, hurling clouds of
electrified gas towards Earth, producing four explosions,
called flares, and spawning storms of high-speed particles in
space.
The largest of the four flares occurred at 9:57 UT
Thursday, March 29 and was rated as an X-class flare, the most
potent designation. The other three flares were rated M-class,
second only to the X-class. An eruption near AR 9393 hurled a
cloud of electrified, magnetic gas towards Earth on Wednesday.
This eruption, called a Coronal Mass Ejection (CME), may cause
auroral (northern and southern lights) displays and magnetic
storm activity when it impacts the Earth's magnetic field
sometime Friday. Another Earthbound CME associated with the
X-class flare was seen at 10:26 UT March 29, and is expected
to arrive on Saturday.
"Sunspots with complex magnetic field structures like
those in AR 9393 can generate big flares, and sure enough, we
just had a powerful X-class flare from this area," said
Dr. Joseph Gurman, NASA project scientist for the Solar and
Heliospheric Observatory spacecraft, one of a fleet of
sun-observing spacecraft now tracking this region and its
activity.
Sunspots are darker areas on the visible surface of the Sun
caused by a concentration of distorted magnetic fields. The
strong magnetic field slows down the flow of heat from the
Sun's interior and keeps sunspots slightly cooler than
their surroundings, causing them to appear dark. The number of
sunspots increases and decreases as the Sun's 11-year cycle of
stormy activity rises and falls. Violent solar activity is
believed to be caused by the release of magnetic energy, and
powerful solar eruptions like CMEs and flares often occur near
the enhanced magnetic field of sunspots.
Solar flares, among the solar system's mightiest eruptions,
are tremendous explosions in the atmosphere of the Sun capable
of releasing as much energy as a billion megatons of TNT.
Caused by the sudden release of magnetic energy, in just a few
seconds flares can accelerate solar particles to very high
velocities and heat solar material to tens of millions of
degrees.
CMEs are clouds of electrified, magnetic gas weighing
billions of tons ejected from the Sun and hurled into space
with speeds ranging from 12 to 1,250 miles per second (about
20 to 2,000 kilometers per second). Depending on the
orientation of the magnetic fields carried by the CME cloud,
Earth-directed CMEs cause magnetic storms by interacting with
the Earth's magnetic field, distorting its shape and
accelerating electrically charged particles (electrons and
atomic nuclei) trapped within.
Severe solar weather is often heralded by dramatic auroral
displays, but magnetic storms are occasionally harmful,
potentially disrupting satellites, radio communications, and
power systems.
Both CMEs and flares are capable of producing storms of
high-velocity particles. CMEs are believed to produce longer
particle storms than flares, storms that sometimes last for
days, as they plow through the slower solar wind at supersonic
speeds, creating a shock wave that accelerates electrically
charged subatomic particles.
A NASA video file with movies and images of this sunspot
will be broadcast on NASA TV Friday, March 30. For more
information on the sunspot, refer to:
