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

Harvard-Smithsonian Center for Astrophysics
Release No.: 03-15
For Release: June 26, 2003

State-Of-The-Art Solar Model Fits Massive 2002 Eruption

Cambridge, MA - As computer power and speed continues to increase,
scientists are developing ever more sophisticated computer models
that can predict the weather, help design cars and planes, and even
evaluate new medicines. Astronomers use models, too - in order to
investigate how solar systems form, how stars are born, even how the
Universe began. 

One particularly relevant subject for modeling is our nearest star,
the Sun. The Sun pours out beneficial light and heat, but also
dangerous energetic particles and radiation. Solar physicists Jun Lin
(Harvard-Smithsonian Center for Astrophysics) and Terry G. Forbes
(University of New Hampshire) have developed a state-of-the-art
computer model for the massive solar eruptions that threaten
satellites, communications networks and power grids. Their model
matched observations by the Smithsonian Astrophysical Observatory's
UltraViolet Coronagraph Spectrometer (UVCS) on the SOHO satellite,
which observed a real-world blast from the Sun in April of 2002,
providing hope that one day such models will predict solar eruptions
and space weather. 

"By building on four decades of modeling work conducted by many
researchers, we have developed a computer code to describe the entire
development of a solar eruption from beginning to end. By improving
our understanding of the physics behind these blasts, we hope to
improve our ability to predict them," said Lin.

Earthly Effects Of Solar Eruptions

The Sun may appear to be a bright, steadily shining orb, but it is
actually a seething cauldron of hot gases prone to violent eruptions.
The most dramatic eruptions are coronal mass ejections (CMEs), in
which giant, bubble-shaped balloons of plasma and magnetic field
lines blast outward at speeds of up to 1,500 miles per second. If an
airplane were able to travel that fast, a trip across the United
States would take only 2 seconds, and a round-the-world flight would
last 20 seconds. CMEs can eject up to 200 billion pounds of matter
into interplanetary space. 

These bursts of plasma can wreak havoc if they impact the Earth. CMEs
have the potential to disable satellites, disrupt pager and cell
phone networks, and knock out electrical power grids. They also pose
a danger to astronauts, particularly future travelers to Mars.

"An astronaut on Mars, unprotected by a strong magnetic field and
thick atmosphere like we have on Earth, could be exposed to a lethal
dose of radiation and ionized particles. All of these reasons show
why it is so important that we understand, and eventually be able to
predict, CMEs," said Lin.

A Successful CME Model

The powerful computer model developed by Lin and Forbes simulates the
evolution of coronal mass ejections. Of particular importance, the
model calculates the final configuration of the CME's magnetic field,
which determines what the effect will be on the Earth - a magnetic
field oriented opposite the Earth's leads to more dramatic and
disruptive impacts.

The Lin & Forbes model is the first to predict that a long current
sheet is a key feature of CMEs. The current sheet is a region where
oppositely directed magnetic fields annihilate one another, in a
process known as magnetic reconnection, releasing magnetic energy to
accelerate and heat the CME as it erupts from the Sun's surface and
blasts outward through the solar corona.

An April 21, 2002 eruption provided an excellent opportunity to
gather data that could be compared to the Lin & Forbes model. A large
suite of instruments on the SOHO, TRACE and RHESSI spacecraft all
observed this eruption in exquisite detail. While TRACE and RHESSI
observed the initiation of the eruption, the UVCS instrument on SOHO
observed this event above the surface in the region of peak
acceleration. Its observations provided direct evidence of the hot
gas identified with the current sheet predicted by the Lin & Forbes
model. This is the strongest evidence yet that the Lin & Forbes model
is an accurate description of how CMEs are produced. UVCS also found
that the shock wave did not form until the CME reached a larger
height, and showed the rapid disruption of the corona as the hot
magnetic bubble predicted by the Lin & Forbes model was accelerated
upwards and pushed the coronal gas aside. 

Lin and his colleagues expect to continue improving and refining
their CME computer model as more is learned about the physics behind
these eruptions.

NOTE TO EDITORS: An animation and spacecraft image of a coronal mass
ejection are available at:
http://cfa-www.harvard.edu/press/pr0315image.html

Headquartered in Cambridge, Massachusetts, the Harvard-Smithsonian
Center for Astrophysics (CfA) is a joint collaboration between the
Smithsonian Astrophysical Observatory and the Harvard College
Observatory. CfA scientists organized into six research divisions
study the origin, evolution, and ultimate fate of the universe.

For more information, contact:

David Aguilar, Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
Phone: 617-495-7462 Fax: 617-495-7468
daguilar{at}cfa.harvard.edu

Christine Lafon
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
Phone: 617-495-7463, Fax: 617-495-7016
clafon{at}cfa.harvard.edu

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

@Message posted automagically by IMTHINGS POST 1.30
---