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Editor
Mike Hollis
Associate Editor
Jarrett Cohen
Consultants
Lara Clemence
Jim Fischer
Jasaun Neff
Website Design
Pamela Ricks
PDF Design
DeAnna Yu
Download a PDF version of the newsletter:
+ CISTO News Winter-Spring 2008
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ISSUE FOCUS ON HELIOPHYSICS |
NCCS Support of Space Exploration:
Improving Space Weather Modeling Required for
Interplanetary Travel
By Jarrett Cohen and Mike Hollis
Part
I: Simulating Coronal Mass Ejections
A coronal mass ejection (CME) is a violent
ejection of plasma–material comprised chiefly
of protons and electrons–from the million-degree
Kelvin solar corona just above the 6,000-degree
Kelvin surface of the Sun. CMEs can propel
up to 100 billion tons of material out into
the solar system (see Figure 3, left). They
tend to originate from active regions associated
with sunspots on the solar surface. These
regions have closed magnetic field lines
that contain the plasma. Thus, the CME must
open these field lines to escape from the
Sun. When the CME ejecta reaches Earth,
it can distort the magnetosphere (the region
dominated by the planet's protective magnetic
field), compressing it on the dayside and
extending the nightside magnetotail. CME
events can disrupt radio transmissions,
cause power grid blackouts, and damage satellites.
 
Figure
3: On the left is an image of a large
coronal mass ejection (CME) taken by the
Solar and Heliospheric Observatory (SOHO).
The occulting disk blocks the Sun so that
SOHO can observe the structures of the
corona (the Sun's atmosphere) in visible
light. The white circle represents the
size and position of the Sun. On the right
is a simulated 3D radiation map of the
corona. Green coloring shows the radio
radiation from a CME-driven shock, while
jets colored yellow and red reveal the
stream structure near the Sun. Simulation
by Joachim Schmidt and Nat Gopalswamy.
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Joachim Schmidt of GSFC's Planetary Magnetospheres
Laboratory and others believe that the triggering
mechanism for a CME is the movement of magnetic field
lines and/or cancellation of magnetic footprint
signatures directly below the coronal mass.
Observations alone cannot distinguish between these
scenarios because one only sees the resultant
radiation at a distance. To theoretically model CMEs,
Schmidt uses 128 processors of Explore, the NCCS'
SGI Altix computer system. He attacks the problem
by simulating a CME-driven collisionless shockwave
on a large scale with one model and employing a
second kinetic model that provides greater detail
on a much smaller scale.
The large-scale model is a magnetohydrodynamics
(MHD) computer code that solves MHD equations
for the bulk motion of the outflowing
plasma that can travel at speeds upwards
of 1,000 kilometers per second. This code
is the Solar Coronal module of the Space
Weather Modeling Framework (SWMF) developed
at the University of Michigan. The SWMF
was initially funded earlier this decade
by the NASA Computational Technologies
Project within CISTO. The small-scale
kinetic model code is one of Schmidt's design
and is a continuing work in progress.
Coupling these models provides three-dimensional
(3D) predictions of the CME signatures
in the radio region of the electromagnetic
spectrum (see Figure 3, right), which
can be validated by arrays of ground-based
radio telescopes here on Earth and radio
receivers on NASA vehicles such as the
interstellar WIND spacecraft and the Solar
and Heliospheric Observatory (SOHO).
Schmidt summarizes his major findings
so far: "There were two schools of thought,
that shockwaves that drive radiation dissipate
very quickly or that they survive over
large timescales and distances in space.
I have determined that solar flares are
much more dissipative compared to the
much longer lived CME-driven shockwaves."
As for future NASA exploration ventures,
Schmidt is working with Joseph Lazio at
the Naval Research Laboratory to design
a dipole radio array for the Moon based
on Schmidt's successful model results–a
space weather station, if you will, for
the Moon. |
Introduction
Part I: Simulating
Coronal Mass Ejections
Part II:
Focusing on Magnetic Reconnection
Part III:
Getting the Ionosphere Model Right
Epilogue
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http://www.nccs.nasa.gov
http:/hsd.gsfc.nasa.gov
http://nasascience.nasa.gov/heliophysics/mission_list |
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