Physical mechanism behind ’sympathetic flares’ on the Sun discovered

WASHINGTON - Scientists have finally uncovered the physical mechanism behind so-called ’sympathetic flares’ on the Sun - thanks to a serendipitous alignment of high-powered spaceborne solar instruments.

The instruments were designed and built by Lockheed Martin.

On August 1st of this year, nearly the entire Earth-facing side of the Sun erupted in a tumult of activity, comprising a large solar flare, a solar tsunami, multiple filaments of magnetism lifting off the solar surface, radio bursts, and half a dozen coronal mass ejections (CMEs).

At the same time, three NASA spacecraft-the Solar Dynamics Observatory (SDO) and the twin Solar Terrestrial Relations Observatory (STEREO) spacecraft-were ideally positioned to capture both the action on the Earth-facing side of the Sun, and most activity around the backside, leaving a wedge of only 30 degrees of the solar surface unobserved.

“The high-quality simultaneous data we received from SDO and the STEREO spacecraft, and our subsequent analysis, enable us to present unambiguous evidence that solar regions up to 160 degrees away are involved in defining the large-scale coronal field topology for flares and CMEs,” said Dr. Carolus Schrijver, of the Solar and Astrophysics Lab at the Lockheed Martin Advanced Technology Center in Palo Alto, and lead author of a paper.

“Moreover, as far as we are aware, this is the first well-documented case that is highly suggestive that the evolution of that distant field, i.e., the flux emergence in one or more of the three active regions behind the eastern limb of the Sun as seen from Earth and SDO, plays an important role in the destabilization of the magnetic field involved in a series of CMEs aimed for Earth.”

The SDO Atmospheric Imaging Assembly (AIA) provides a major advance in the ability of physicists to observe the solar corona: full-Sun 4096 x 4096 images with 0.6 arcsec pixels, in temperatures ranging from chromospheric around 10,000 K up to about 10 million K, with images every 12 seconds, without interruption.

The instrument design enables the tracing of perturbations over long distances, even if short-lived or occurring at, or changing across, widely different temperatures. At the time of the August 1st observations, the STEREO spacecraft were each approaching quadrature relative to the Sun-Earth line, thus providing perspectives on activity on most of the eastern and western hemispheres relative to Sun-Earth line. Moreover, the SDO Helioseismic and Magnetic Imager (HMI), combined with a computational model of full-sphere flux-transport on the Sun, and global coronal field modeling, revealed the long-distance magnetic connections with fair fidelity.

“We’ve reached a turning point in our ability to forecast space weather,” said Dr. Alan Title of the ATC, and co-author of the paper presented.

“We now have evidence that multiple events can be triggered by other events that occur in regions that cannot be observed from Earth orbit. This gives us a new appreciation of why solar flare and CME predictions have been less than perfect.

As we seek to understand the causes of eruptive and explosive events that will improve our ability to forecast space weather, it is clear that we must be able to analyze most of the evolving global solar field, if not all of it.”

The results have been presented at the American Geophysical Union meeting in San Francisco. (ANI)