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"Focused" solar explosions get hotter (Forwarded)



 
 
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Old April 4th 08, 05:00 PM posted to sci.space.news
Andrew Yee[_1_]
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Default "Focused" solar explosions get hotter (Forwarded)

Rani Gran / Bill Steigerwald
NASA Goddard Space Flight Center, Greenbelt, Md. April 2, 2008
301-286-2483 / 5017

PRESS RELEASE: 08-30

"FOCUSED" SOLAR EXPLOSIONS GET HOTTER

A NASA-funded researcher has discovered that solar flares -- explosions
in the atmosphere of the sun -- get much hotter when they stay
"focused".

"A flare typically divides its energy between directly heating the solar
atmosphere and accelerating particles," said Dr. Ryan Milligan of the
Oak Ridge Association of Universities, Tennessee, who is stationed at
NASA's Goddard Space Flight Center in Greenbelt, Md. "This flare seemed
to focus on one task, devoting all its energy to heating, allowing it to
become millions of degrees hotter than its multi-tasking cousins." The
result will be presented Wednesday, April 2 at the Royal Astronomical
Society's National Astronomy Meeting 2008 at Queen's University,
Belfast, United Kingdom.

Solar flares are caused by the sudden release of magnetic energy. The
largest can release as much energy as a billion one-megaton nuclear
bombs. However, the flare observed in this study was a less powerful
"micro" flare. NASA researchers want to understand flares because they
generate radiation that can be hazardous to unprotected astronauts, like
those walking on the surface of the moon.

Flares normally occur above loops of electrically conducting gas, called
plasma, in the sun's atmosphere. When a typical flare goes off, it heats
the plasma and sends beams of electrons racing down the sides of the
loops. The electron beams evaporate more plasma from the sun's visible
surface, which expands back up the loops.

"This evaporated plasma has traditionally been believed to be the source
of the hottest temperatures seen in solar flares," said Milligan.
"However, the flare in this new observation reached a temperature of
almost 27 million degrees Fahrenheit -- some nine million degrees hotter
than expected for a flare of this size -- without any evidence for beams
of accelerated electrons."

Milligan used the Reuven Ramaty High Energy Solar Spectroscopic Imager
(RHESSI) and Hinode spacecraft to make his observation of the microflare
on June 7, 2007. RHESSI revealed that the flare had a peak temperature
of 27 million degrees, and also that the flare showed no evidence for
high-energy electrons. Hinode was able to show the effects of the energy
released at various layers in the solar atmosphere. In particular, the
Extreme-ultraviolet Imaging Spectrometer instrument was used to detect
signatures of plasma evaporation from the sun's surface through Doppler
shifts of emission lines. The low-velocities observed confirmed the
RHESSI observation that high-energy electrons were not present.

"If our assumption is correct, then this result tells us that the energy
released during a solar flare is more efficient at achieving a higher
temperature if the energy is used to directly heat the plasma in the
sun's atmosphere, instead of being divided between heating and particle
acceleration. This very effect has recently been shown in computer
simulations of energy release during microflares," said Milligan.

The research was funded by the NASA Postdoctoral Program administered by
the Oak Ridge Association of Universities, Tennessee.

Hinode is a Japanese mission, collaborating with NASA and the Science
and Technology Facilities Council, United Kingdom, as international
partners. The RHESSI project is a NASA Small Explorer mission managed by
the Space Sciences Laboratory of the University of California, Berkeley.
The Explorers Program Office at Goddard provides management and
technical oversight under the direction of the Heliophysics Division of
the Science Mission Directorate at NASA Headquarters in Washington, D.C.

For an image, refer to:

http://www.nasa.gov/centers/goddard/...ed_flares.html
 




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