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'The Non-Potentiality of Active-Region Coronae and the Dynamics of the Photospheric Magnetic Field'


Image from the TRACE Satellite


Image of typical SOHO observations


Read More (PDF)

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Scientists funded by NASA have made big strides in learning how to forecast "all clear" periods, when severe space weather is unlikely. The forecasts are important because radiation from particles from the sun associated with large solar flares can be hazardous to unprotected astronauts, airplane occupants and satellites.

"We have a much better insight into what causes the strongest, most dangerous solar flares, and how to develop forecasts that can predict an 'all clear' for significant space weather, for longer periods" - Dr. Karel Schrijver , Lockheed Martin Advanced Technology Center (ATC), Palo Alto, California. He is lead author of a paper about the research published in the Astrophysical Journal.

Solar flares are violent explosions in the atmosphere of the sun caused by the sudden release of magnetic energy. Like a rubber band twisted too tightly, stressed magnetic fields in the Suns atmosphere (corona) can suddenly snap to a new shape. They can release as much energy as one, 10 billion megaton nuclear bomb.

Predicting space weather is a complicated problem. Solar forecasters focus principally on the complexity of solar magnetic field patterns to predict solar storms. This method is not always reliable, because solar storms require additional ingredients to occur. It has long been known large electrical currents must be present to power flares.

Insight into the causes of the largest solar flares came in two steps.
"First, we discovered characteristic patterns of magnetic field evolution associated with strong electrical currents in the solar atmosphere. It is these strong electrical currents that drive solar flares" - Dr. Marc DeRosa, Advanced Technology Center ,co-author of the paper

Subsequently, the authors discovered the regions most likely to flare had new magnetic fields merge into them that were clearly out of alignment with the existing field. This emerging field from the solar interior appears to induce even more current as it interacts with the existing field.

The team also found flares do not necessarily occur immediately upon the emergence of a new magnetic field. Apparently the electrical currents must build up over several hours before the fireworks start. Predicting exactly when a flare will happen is like studying avalanches. They occur only after enough snow built up. Once the threshold is reached, the avalanche can happen anytime by processes not yet completely understood.

"We found the current-carrying regions flare two to three times more often than the regions without large currents. Also, the average flare magnitude is three times greater for the group of active regions with large current systems than for the other group" - Dr. Karel Schrijver.

The researchers made the discovery by comparing data about magnetic fields on the Suns surface to the sharpest extreme-ultraviolet images of the solar corona. The magnetic maps were from the Michelson Doppler Imager (MDI) instrument on board Solar and Heliospheric Observatory (SOHO) spacecraft. SOHO is operated under a cooperative mission between the European Space Agency and NASA.

The corona images were from the NASA Transition Region and Coronal Explorer spacecraft (TRACE). The team also used computer models of a three-dimensional solar magnetic field without electrical currents based on SOHO images. Differences between images and models indicated the presence of large electrical currents.

"This is a result that is more than the sum of two individual missions. It's not only interesting scientifically, but has broad implications for society." - Dr. Dick Fisher, Director of NASA's Sun-Solar System Connection Division.

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Scientists using the TRACE and SOHO satellites compared images of the surface of the sun with readings of its magnetic fields, have managed to determine when such an electric current with an `opposite` orientation climbs to the surface from inside the Sun it forms an active region on the Sun's surface.

The magnetic field on the surface would show if a solar storm would be formed in that region. If the magnetic field appeared different from the surface, it would mean that a solar flare was on the way.

However, the researchers still can't tell exactly when it will actually erupt.

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Everyone is familiar with changes in the weather on Earth. But "weather" also occurs in space. Just as it drives weather on Earth, the Sun is responsible for disturbances in our space environment.
Besides emitting a continuous stream of plasma called the solar wind, the Sun periodically releases billions of tons of matter in what are called coronal mass ejections. These immense clouds of material, when directed towards Earth, can cause large magnetic storms in the magnetosphere and the upper atmosphere.
The term space weather generally refers to conditions on the Sun and in the solar wind, magnetosphere, ionosphere, and thermosphere that can influence the performance and reliability of space-borne and ground-based technological systems and can endanger human life or health.

http://lws.gsfc.nasa.gov/

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Briefing Participants:
Dr. Richard Fisher, Director, NASA Sun-Solar System Connection Division, Washington
Dr. Karel Schrijver, Senior Staff Physicist, Lockheed Martin Solar and Astrophysics Laboratory, Palo Alto, California.
Dr. Marc DeRosa, Research Physicist, Lockheed Martin Solar and Astrophysics Laboratory, Palo Alto, California.
Dr. Joseph Kunches, NOAA Space Environment Center Director, Boulder, Colorado.

Dr.Fisher was appointed as the Director of the Sun-Earth Connection Division in March 2002.
Dr. Fisher has overall responsibility for developing policy and providing guidance for NASA's program to understand the physics of the variable Sun and its influence on the heliosphere, solar system plasmas, the upper atmospheres and magnetospheres of planets, especially the Earth, and the origin of cosmic rays.
Dr. Karel Schrijver is Staff Physicist at the Lockheed Martin Advanced Technology Center. Dr. Schrijver is a member of the solar and astrophysics group at Lockheed's Palo Alto Research Laboratory. His current work focuses on analysis of data from the Michelson Doppler Imager on the Solar and Heliospheric Observatory (SOHO) and from the Transition-Region and Coronal Explorer (TRACE; for which he also coordinates the daily science operations).



A present an updating forecast of photospheric and coronal magnetic fields, (based on a full-sphere surface-field dispersal model combined with a potential-field source-surface model) is based on SOHO/MDI magnetograms, that are assimilated into a model that evolves the photospheric field on the entire sphere subject to large-scale flows and supergranular dispersal.
Current helioseismic farside information uses an experimental algorithm to translate time delays into magnetic fluxes on the farside central meridian.



Photospheric magnetic field projections for more than one full solar rotation (from one week in the past to three weeks into the future) are currently possible.



The Sun's magnetic field connects the different domains in its atmosphere. The visible surface (green), at about 10,000 degrees F, with dark sunspots where the field is strong and coherent, and faintly showing bright kernels where the field is about half as strong and broken up. Around them the seething motions of the convection form tiny cells called granules.



Credit: Swedish Royal Academy of Sciences, TRACE team, NASA, Lockheed Martin
The images were taken at the Swedish Solar Observatory on La Palma, Spain (lower three), and with the Transition Region and Coronal Explorer (top).



The second image (blue) shows the emission from the chromosphere. This domain of the solar atmosphere extends up to some 4,000 miles above the solar surface. It is transparent to most of the light emitted by the solar photosphere, but opaque or even brightly emitting at a select set of specific colours (wavelengths). It earned its name, which means ''coloured sphere,'' because it is seen as a colourful ring around an eclipsed Sun. It has a temperature of approximately 18,000 degrees F. The sunspots remain dark, but the smaller magnetic concentrations now emit much more brightly in the light of ionized calcium ions (Ca II K).

The third image (yellow) from below shows the Sun in light of neutral hydrogen gas. Because hydrogen is the most abundant element in the Sun, its atoms contribute over a larger range of heights than images taken in the light of other elements at a comparable temperature. It is for that reason that the image reveals segments of the magnetic field with a three-dimensional character, rather than appearing as a thin slice through a fixed level in the atmosphere. Here the fields can be seen to lean away from the strong field in the sunspot in the centre.

The top image (red) shows the highest, hottest domain of the solar atmosphere, called the corona, with emission from gas at a million degrees. The atmosphere is completely transparent at these wavelengths, so we see the field at a range of heights, thus revealing fans and curtains of emission from hot, ionized gas that is captured within the magnetic field.

Operational Space Weather Support for the Commercial Airlines (pdf)

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NASA Announces Breakthrough in Space Weather Forecasting

Researchers from NASA, the National Oceanic and Atmospheric Administration (NOAA), and the Lockheed Martin Advanced Technology Centres Solar and Astrophysics Laboratory (LMSAL) will present new findings on space weather during a media teleconference on Tuesday, Aug. 16 at 18:00 GMT.

Scientists funded by NASA's Living With a Star program have made a significant discovery that will help everyone from satellite operators and airlines to astronauts living and working in space.

Images and graphics supporting the conference will be posted on the Internet at:
http://www.nasa.gov/vision/universe/solarsystem/clear_weather.html (on Aug. 16)

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