This Echo is READ ONLY !   NO Un-Authorized Messages Please!
 ~~~~~~~~~~~~~~~~~~~~~~~~   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Bill Steigerwald                    April 10, 2003
NASA Goddard Space Flight Center
(Phone: 301 286 5017)
William.A.Steigerwald{at}nasa.gov


Release: 03-36

GIANT SOLAR TADPOLES BORN IN EXPLOSION

Dark features resembling Earth-sized tadpoles were seen swimming in 
the atmosphere of the Sun after it was heated to millions of degrees 
following an enormous explosion, according to scientists who made the 
observation using NASA's Transition Region and Coronal Explorer 
(TRACE) spacecraft.

"This is the best view yet of these enigmatic shapes," said Dr. 
Edward Deluca of the Harvard-Smithsonian Astrophysical Observatory 
(SAO), Cambridge, Mass., who is a co-author of a paper on the 
observation to be submitted to the Astrophysical Journal in September 
2003. The observation is expected to shed light on the physics of 
magnetic reconnection, the process believed to power solar 
explosions, which occasionally disrupt satellites and power systems. 
The result is presented this week as a poster at the American 
Geophysical Union meeting in Nice, France.

The explosion on April 21, 2002, was an "X-class" solar flare, the 
most powerful kind, releasing about as much energy as a billion 
one-megaton nuclear bombs. It was also associated with a coronal mass 
ejection (CME), a multi-billion ton eruption of electrified gas 
(plasma) into space.

The tadpoles are mysterious in part because of their behavior. "In 
the vicinity of a solar flare associated with a CME, most matter is 
moving away from the solar surface, but the tadpoles move downward at 
initial speeds between 30 and 600 kilometers per second (about 19 to 
373 miles/sec.), something you don't expect," said Dr. David McKenzie 
of Montana State University - Bozeman, who has observed these 
features many times before at lower resolution with the Soft X-ray 
Telescope on board the Japanese Yohkoh spacecraft.

TRACE observes ultraviolet light from iron atoms in solar plasma at 
two temperatures: 1.5 million degrees Celsius (2.7 million 
Fahrenheit) and 10 million degrees Celsius (18 million Fahrenheit). 
Theories explaining the tadpoles included the possibilities that they 
were dense blobs of plasma, with a different temperature than what 
TRACE could detect, that absorbed ultraviolet light from plasma 
behind them or that they were voids with hardly any 
ultraviolet-emitting plasma in them.

While both circumstances would create dark regions in TRACE images, 
the new data, coordinated with observations from other spacecraft, 
have now convinced scientists that the tadpoles are superheated 
magnetic voids in the plasma. The voids are formed when magnetic 
fields that lace the solar atmosphere reconnect and snap back to the 
surface following a flare and CME. According to the analysis 
presented today, the tadpoles appear dark simply because there is 
very little material in them.

"Imagine a hot-air balloon lifting off the ground and stretching 
elastic tethers placed over its top," said McKenzie. "The tethers are 
like the solar magnetic field, and the balloon represents the CME. As 
the balloon rises, the elastic tethers stretch, get pulled together, 
and start to tangle underneath the balloon. If the tethers were to 
behave like solar magnetic fields, instead of simply breaking, broken 
tethers would reconnect to other broken tethers, forming new 
connections (magnetic reconnection)."

"If this tangling and reconnection goes on long enough, pieces of 
elastic tethers that are connected to the ground (the solar surface) 
connect to other 'grounded' segments, and subsequently snap back down 
to the ground. Their snapping downwards gives the tadpoles a downward 
motion, as the stretched magnetic fields relax to form long rows of 
arches called arcades. Pieces connected to the balloon get tied to 
other 'balloon-connected' segments and are carried off as magnetic 
fields embedded in the CME."

Apparently, the tadpoles are reconnected magnetic tubes, seen in 
cross section. The tube's magnetic pressure temporarily keeps the 
surrounding hot plasma out, forming a void. With very little or no 
plasma inside the tubes, there is no ultraviolet emission there, and 
they appear as dark blobs (tadpoles) when seen in cross section. 
After the reconnection, the magnetic tubes shrink away from the 
departing CME. As the tubes move downward, the voids gradually fill 
with hot plasma from underneath and disappear.

TRACE is able to take more detailed pictures faster, allowing 
scientists to better characterize the behavior of the tadpoles. "No 
one knows exactly how magnetic reconnection works. The TRACE 
observations give us constraints, which allow us to select from among 
many competing theories," said Deluca.

"Improved understanding of magnetic reconnection will help us better 
understand when a highly-magnetized region of the Sun will suddenly 
erupt as a flare or CME," added Deluca.

Other members of the TRACE team include lead author Mr. Fenwick 
Cooper, a Ph.D. student at the University of Warwick, The United 
Kingdom, Prof. Valery Nakariakov, also of the University of Warwick, 
and Dr. Dan Seaton of SAO.

For images and more information, refer to:
http://www.gsfc.nasa.gov/topstory/2003/0411tadpoles.html

-end-

 - END OF FILE -
==========

@Message posted automagically by IMTHINGS POST 1.30
---