The Great Solar Eruption

Now that we are able to lookclosely, we are finding out just now active the sun can be.  No one imagined this or that such an eventwould go unnoticed on Earth but from our observation gear now in place.

The importance of this eruptionis not so much the event itself however unprecedented as the discovery ofdirect linkage on a global basis for the large events.  This completely resets our models and generalthinking.

I recall when we expected littlefrom the sun in new data.  Now we arelooking at a variable star up close in 360 degrees and getting all the actionwe could ever desire.

The miracle is how well shieldedwe are and have been for billions of years.

Global Eruption Rocks theSun

Dec. 13, 2010:  On August 1,2010, an entire hemisphere of the sun erupted. Filaments of magnetism snappedand exploded, shock waves raced across the stellar surface, billion-ton cloudsof hot gas billowed into space. Astronomers knew they had witnessed somethingbig.

It was so big, it may have shattered old ideasabout solar activity.

"The August 1st event really opened oureyes," says Karel Schrijver of Lockheed Martin’s Solar and AstrophysicsLab in Palo Alto,CA. "We see that solar storms can be global events, playing out on scaleswe scarcely imagined before."

Click to play an extreme ultravioletmovie of the August 1st global eruption. Different colors represent differentplasma temperatures in the range 1.0 to 2.2 million K. Credit: Solar DynamicsObservatory.

For the past three months, Schrijver has beenworking with fellow Lockheed-Martin solar physicist Alan Title to understandwhat happened during the "Great Eruption." They had plenty of data:The event was recorded in unprecedented detail by NASA's Solar DynamicsObservatory and twin STEREO spacecraft. With several colleagues present to offercommentary, they outlined their findings at a press conference today at theAmerican Geophysical Union meeting in San Francisco.

Explosions on the sun are not localized orisolated events, they announced. Instead, solar activity is interconnected by magnetismover breathtaking distances. Solar flares, tsunamis, coronal massejections--they can go off all at once, hundreds of thousands of miles apart,in a dizzyingly-complex concert of mayhem.

"To predict eruptions we can no longerfocus on the magnetic fields of isolated active regions," says Title,"we have to know the surface magnetic field of practically the entire sun."
This revelation increases the work load forspace weather forecasters, but it also increases the potential accuracy oftheir forecasts.

"The whole-sun approach could lead tobreakthroughs in predicting solar activity," commented Rodney Viereck ofNOAA's Space Weather Prediction Center in Boulder, CO. "This in turn wouldprovide improved forecasts to our customers such as electric power gridoperators and commercial airlines, who could take action to protect theirsystems and ensure the safety of passengers and crew."

In a paper they prepared for the Journal ofGeophysical Research (JGR), Schrijver and Title broke down the Great Eruptioninto more than a dozen significant shock waves, flares, filament eruptions, andCMEs spanning 180 degrees of solar longitude and 28 hours of time. At first itseemed to be a cacophony of disorder until they plotted the events on a map ofthe sun's magnetic field.

Title describes the Eureka! moment: "We saw that allthe events of substantial coronal activity were connected by a wide-rangingsystem of separatrices, separators, and quasi-separatrix layers." A"separatrix" is a magnetic fault zone where small changes insurrounding plasma currents can set off big electromagnetic storms.

Locations of key events are labeled in thisextreme ultraviolet image of the sun, obtained by the Solar DynamicsObservatory during the Great Eruption of August 1st. White lines trace thesun's magnetic field. Credit: K Schrijver & A. Title. [larger image]

Researchers have long suspected this kind ofmagnetic connection was possible. "The notion of 'sympathetic' flares goesback at least three quarters of a century," they wrote in their JGR paper.Sometimes observers would see flares going off one after another--likepopcorn--but it was impossible to prove a link between them. Arguments in favorof cause and effect were statistical and often full of doubt.

"For this kind of work, SDO and STEREOare game-changers," says Lika Guhathakurta, NASA's Living with a StarProgram Scientist. "Together, the three spacecraft monitor 97% of the sun,allowing researchers to see connections that they could only guess at in thepast."

To wit, barely two-thirds of the August eventwas visible from Earth, yet all of it could be seen by the SDO-STEREO fleet.Moreover, SDO's measurements of the sun's magnetic field revealed directconnections between the various components of the Great Eruption—no statisticsrequired.

Much remains to be done. "We're stillsorting out cause and effect," says Schrijver. "Was the event one bigchain reaction, in which one eruption triggered another--bang, bang, bang--insequence? Or did everything go off together as a consequence of some greaterchange in the sun's global magnetic field?"

Further analysis may yet reveal the underlyingtrigger; for now, the team is still wrapping their minds around the globalcharacter of solar activity. One commentator recalled the old adage of threeblind men describing an elephant--one by feeling the trunk, one by holding thetail, and another by sniffing a toenail. Studying the sun one sunspot at a timemay be just as limiting.

"Not all eruptions are going to beglobal," notes Guhathakurta. "But the global character of solaractivity can no longer be ignored."

As if the sun wasn't big enough already….

No comments:

Post a Comment