Fast-moving solar eruptions are overtaking and devouring
their slower kin. The cosmic collisions apparently create
strange radio fireworks that can be heard by astronomers.

Using the Solar and Heliospheric Observatory (SOHO) spacecraft
from NASA and the European Space Agency (ESA), the team linked
the radio outbursts to images of the solar eruptions, known as
Coronal Mass Ejections (CMEs).

Solar eruptions directed toward Earth are potentially harmful
to advanced technology, including communications and power
systems, and this cannibalistic behavior may result in longer
magnetic storms. These collisions change the speed of the
eruption, which is important for space weather prediction
because it alters estimated arrival time of Earthbound coronal
ejections.

“Coronal Mass Ejection cannibalism is the most violent form of
interaction between CMEs,” said Dr. Natchimuthuk Gopalswamy,
lead author of a research paper presented today during a
meeting of the European Geophysical Society in Nice, France.
“This happens when a slow CME is expelled before a fast one
from the same general region on the Sun. The fast CME simply
gobbles up the slow CME, resulting in a single CME beyond the
region of interaction.”

Gopalswamy, a research professor with The Catholic University
of America, Washington, DC, is stationed at NASA’s Goddard
Space Flight Center, Greenbelt, MD. He presented the research
with his colleagues from Goddard, Catholic University and the
Naval Research Laboratory.

Coronal mass ejections are clouds of electrified, magnetic
gas, weighing billions of tons, ejected from the Sun and
hurled into space at speeds of 12 to 1,250 miles per second.
Depending on the orientation of the magnetic fields carried by
the ejection cloud, Earth-directed eruptions cause magnetic
storms by interacting with the Earth’s magnetic field,
distorting its shape and accelerating electrically charged
particles trapped within.

The researchers believe cannibal eruptions may be the source
of “complex ejecta” CME clouds, larger and more complex in
structure than typical eruptions. These traits cause complex
ejecta CMEs to trigger protracted magnetic storms when they
envelop the Earth.

Severe solar weather is often heralded by dramatic auroral
displays (northern and southern lights), but magnetic storms
are occasionally harmful, potentially affecting satellites,
radio communications and power systems. Understanding what
happens to ejection clouds on their way to Earth is important
in assessing their impact on the near-Earth space environment.

Observations from SOHO’s Radio and Plasma Wave experiment
revealed occasional intense bursts of emission originating far
away from the Sun. When Gopalswamy and his colleagues were
searching for the source of these radio outbursts, they
discovered the ejection interaction, which produces high-
energy electrons and cause the radio outbursts. After the
initial discovery, 21 cannibalistic ejections have been
identified since April 1997. There may be even more events
that aren’t detected because they are less energetic and do
not produce a radio outburst, according to the researchers.

“Collisions between CMEs may be more common than previously
thought and may play a key role in determining the
interplanetary traffic of CMEs,” Gopalswamy added.

The astronomers expect an increased rate of ejection
interaction during the current peak in the 11-year cycle of
violent solar activity, called solar maximum, because more
ejections are expelled in quick succession during a solar
maximum. During solar minimum, only one ejection per every
other day is common; during maximum, several ejections occur
in a day.

The cooperative SOHO project is part of NASA’s and ESA’s Solar
Terrestrial Science Program (STSP), comprising of SOHO and
CLUSTER. SOHO was launched Dec. 2, 1995. The SOHO spacecraft
was built in Europe, and instruments were provided by European
and American scientists.

For images and background information on the Internet, see:

http://www.gsfc.nasa.gov/GSFC/SpaceSci/sunearth/cannibalcme.ht
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