Ring Around The Sun by roq91753

VIEWS: 0 PAGES: 3

									Ring Around The Sun
TACC’s Ranger supports corona simulation in advance of solar eclipse

                                                   August 1, 2008 Total Solar Eclipse




Comparison between the predicted eclipse corona from the MHD model and n image taken by Robert Stephens in Yuwi, China. The eclipse imae is a
composit of 13 images with exposers from 1/2000 second to 2 seconds. The images are oriented so that solar north points vertically up. It is evident that
the bright reatures correspond to regions with closed magnetic field lines. Although the model does not reproduce the high-resolution features of the
corona, the locations of the major streamers are predicted reasonable well.



“A time of eclipse is a special time to see the sun’s                          Putting a thoroughly modern spin on the age-old tra-
corona,” solar physicist Zoran Mikic said. “Normally                           dition of forecasting eclipses, Mikic and his team used
you can’t see the corona with the naked eye, because                           Ranger at the Texas Advanced Computing Center
it’s about a million times less bright than the light                          (TACC), one of the world’s most powerful supercom-
coming from the photosphere. But during an eclipse,                            puters for open science research, to predict the spe-
the moon obstructs most of that light, and you see the                         cific dimensions of the solar eclipse seen in parts of
corona — that is what people are in awe of.”                                   the Northern hemisphere on August 1st, 2008. Their
                                                                               computations accurately predicted the size and shape
The ghostly crown that encircles the sun during an                             of the corona, achieving more than twice the resolu-
eclipse is an astonishing sight, shaped by the strong                          tion and accuracy of previous simulations.
magnetic field in the sun’s atmosphere, known as the
corona. Working for Science Applications Interna-                              The predictions represent more than academic show-
tional Corporation (SAIC), Mikic and his group have                            manship, Mikic says. “We want to determine, from a
studied the coronal region for two decades. During                             deep physics understanding, how the physical prop-
much of that time they have been making predictions                            erties of the corona come about, and also understand
about the appearance of the corona during an eclipse                           from a practical point of view how this very hot gas
as a way to test complex, three-dimensional computa-                           comes out of the sun and streams into space as the
tional models of the sun against visible, commonsense                          solar wind.”
reality.

For more information, please contact:
Faith Singer-Villalobos, Public Relations, faith@tacc.utexas.edu, 512.232.5771                                                              Page 1 of 3
Ring Around The Sun
The behavior of the corona is not just a stellar af-                   Solar and Heliospheric Observatory (SOHO); others
fair, after all. The twisting streams of magnetic fields               are based on the equations of physics. In the simplest
and plasma eventually lose their stability and erupt                   of cases, these equations can be solved by analytical
outward in what are called coronal mass ejections                      methods, but in general, they make for the kind of
(CMEs).                                                                problem that only a supercomputer can handle.

“That blob of plasma becomes detached from the sun,                    “The aurora borealis, or the Northern Lights, is the
is captured by the solar wind, and if it’s headed in the               most beautiful manifestation of coronal mass ejec-
direction of the earth, it will interact with the earth’s              tions. But up in space, these same particles can dam-
magnetic field,” Mikic explained. “This can cause                      age satellites or even harm astronauts. And on earth,
charged particles to enter the earth’s atmosphere,                     they can induce ground currents that are sometimes
which has consequences.”                                               large enough to burn out transformers on a large
                                                                       scale.”
The natural fireworks show, known as aurora borea-
lis, or the Northern Lights, is caused by the transmis-                Zoran Mikic, solar physicist at Science Applications
sion of ions from the corona into the upper atmo-                      International Corporation (SAIC)
sphere.
                                                                       Five years ago, Mikic switched to a new magneto-
“That’s the most beautiful manifestation of coronal                    hydrodynamic (MHD) model, in part because of the
mass ejections,” Mikic said. “But up in space, these                   availability of high-performance computing systems
same particles can damage satellites or even harm                      that could simulate more complex physical phenom-
astronauts. And on earth, they can induce ground                       ena. “We’ve been improving how we describe the en-
currents that are sometimes large enough to burn out                   ergy transport in the corona,” Mikic reported. “That
transformers on a large scale.”                                        makes a big effect on predicting what the solar wind
                                                                       looks like and its properties.”
This happened in 1989, when a CME is believed
to have caused a blackout through much of North                        Mikic’s 2006 eclipse prediction of the corona, using
America. So, beyond general scientific interest, Mi-                   the new model, was widely reported as a break-
kic has a compelling reason to study the corona and                    through for the field. Now, two years later, working
to model its activity: his research helps the National                 with TACC, Mikic has produced simulations with far
Aeronautics and Space Administration (NASA) and                        greater resolution than the previous prediction.
the National Science Foundation (NSF) predict when
and where coronal mass ejections might occur.                          “On Ranger, we’ve done our biggest calculation ever.
                                                                       We used over 16 million mesh points, which is prob-
To simulate the corona, Mikic uses mathematical                        ably twice, maybe three times as much as we’ve done
models that combine equations for the temperature                      before. That makes a big difference,” Mikic said. “The
and density of the corona, the magnetic and electrical                 large-scale structure of the sun is not going to change
fields of the sun, the velocity of the plasma, as well as              very much, but we’re seeing much finer detail than
other factors. Some of this information is provided by                 we had previously. That structure, that we’re able to
space monitoring devices, like the magnetograph data                   resolve, translates into features of the corona that we
from the Michelson Doppler Imager (MDI) on the                         didn’t see before.”



For more information, please contact:
Faith Singer-Villalobos, Public Relations, faith@tacc.utexas.edu, 512.232.5771                                     Page 2 of 3
Ring Around The Sun
His recent eclipse prediction used 4,368 processors                    Ranger is a key resource of the NSF TeraGrid (www
on Ranger and ran continuously for almost four days                    teragrid.org), a nationwide network of people, resources
[see full statistics]. The dedicated use of thousands of               and services, also sponsored by the NSF Office of Cyberin-
parallel processors allowed Mikic to make his predic-                  frastructure, which enables discovery in U.S. science and
tion closer in time to the event than before, increas-                 engineering. The TeraGrid provides scientists and research-
ingly the probability of an accurate guess. “You want                  ers expertise in and access to large-scale computing power,
to do it at the last moment so you can use the latest                  networking, data-analysis, and visualization systems.
observed magnetic fields, and still have a prediction
that’s useful,” he said.                                               Aaron Dubrow
                                                                       Texas Advanced Computing Center
The ability to forecast space weather events on a                      Science and Technology Writer
routine, day-to-day basis in an accurate way is still a                October 19, 2008
long way off, Mikic says, but there’s a big push in the
scientific community to develop the methods to do so.
“The whole field is striving to do that, but it’s some-
thing that will take decades to put into practical use.”

For the time being, Mikic’s eclipse predictions help
to develop models that forecasters at NASA and the
Space Weather Prediction Center can use to predict
what’s going to happen to the sun and disseminate
the best information available to satellite operators
and airlines.

Mikic provided a more down-to-earth explanation for
his predictions as well. “Eclipses are beautiful things
and are seen by many people, so there’s a human ele-
ment to these predictions and we’ve built a tradition
making them,” Mikic said. “For us, it’s a special thing
to do.”

                               ###

The Ranger supercomputer is funded through the National
Science Foundation (NSF) Office of Cyberinfrastructure
“Path to Petascale” program. The system is a collaboration
among the Texas Advanced Computing Center, The Uni-
versity of Texas at Austin’s Institute for Computational
Engineering and Science, Sun Microsystems, Advanced
Micro Devices, Arizona State University, and Cornell
University.



For more information, please contact:
Faith Singer-Villalobos, Public Relations, faith@tacc.utexas.edu, 512.232.5771                                        Page 3 of 3

								
To top