On August 1, 2010, an entire hemisphere of the sun erupted. Filaments of magnetism snapped and exploded, shock waves raced across the stellar surface, billion-ton clouds of hot gas billowed into space. Astronomers knew they had witnessed something big.
It was so big, it may have shattered old ideas about solar activity.
“The August 1st event really opened our eyes,” says Karel Schrijver of Lockheed Martin’s Solar and Astrophysics Lab in Palo Alto, CA. “We see that solar storms can be global events, playing out on scales we scarcely imagined before.”
For the past three months, Schrijver has been working with fellow Lockheed-Martin solar physicist Alan Title to understand what happened during the “Great Eruption.” They had plenty of data: The event was recorded in unprecedented detail by NASA’s Solar Dynamics Observatory and twin STEREO spacecraft. With several colleagues present to offer commentary, they outlined their findings at a press conference today at the American Geophysical Union meeting in San Francisco.
Explosions on the sun are not localized or isolated events, they announced. Instead, solar activity is interconnected by magnetism over breathtaking distances. Solar flares, tsunamis, coronal mass ejections–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 longer focus 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 for space weather forecasters, but it also increases the potential accuracy of their forecasts.
“The whole-sun approach could lead to breakthroughs in predicting solar activity,” commented Rodney Viereck of NOAA’s Space Weather Prediction Center in Boulder, CO. “This in turn would provide improved forecasts to our customers such as electric power grid operators and commercial airlines, who could take action to protect their systems and ensure the safety of passengers and crew.”
In a paper they prepared for the Journal of Geophysical Research (JGR), Schrijver and Title broke down the Great Eruption into more than a dozen significant shock waves, flares, filament eruptions, and CMEs spanning 180 degrees of solar longitude and 28 hours of time. At first it seemed to be a cacophony of disorder until they plotted the events on a map of the sun’s magnetic field.
Title describes the Eureka! moment: “We saw that all the events of substantial coronal activity were connected by a wide-ranging system of separatrices, separators, and quasi-separatrix layers.” A “separatrix” is a magnetic fault zone where small changes in surrounding plasma currents can set off big electromagnetic storms.
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