Violent eruptions on the sun that threatened power grids and radio signals on Earth last spring were rooted in convulsions of magnetic energy more than 100,000 miles beneath the solar surface, scientists are discovering.
Their observations from a sensitive satellite-borne instrument that measures the sun's most turbulent events indicate that the sun's behavior is far more complex and dynamic than researchers had ever thought, a team of Stanford University solar physicists reported Monday.
The solar storms, which they have been monitoring for five years, were exceptionally powerful this past spring. The storms formed one vast "active region" of linked eruptions called solar flares that stretched for 150,000 miles - more than 18 times the diameter of Earth - over the sun's surface.
As the sun's surface seethed and shuddered like bubbling lava inside a volcano's crater, the satellite's instrument measured its pressure pulses much the way earthquake scientists analyze seismic tremors along an active fault zone. The technique, in fact, is known as helioseismology.
Three members of the Stanford research team reported on their findings in San Francisco Monday as more than 9,000 scientists began gathering at the Moscone Center for the annual fall meeting of the American Geophysical Union, which continues through this week.
Philip Scherrer, Alexander Kosovichev and Junwei Zhao examined the sun's interior with an instrument aboard the spacecraft called SOHO, the Solar and Heliospheric Observatory now orbiting a million miles from Earth. It carries an instrument called the Michaelson Doppler Imager that monitors solar sound waves 24 hours a day.
Their observations found that last spring's huge solar flares and the burst of ionized gas called a coronal mass ejection were the most powerful in 25 years, Scherrer and Kosovichev said.
It was an unexpected event, because the sun is known to go through an 11-year cycle of activity, and this year is actually seeing the end of the most active period, known as "solar maximum." Sunspots and flare activity will be declining now for five years or so.
Using the same instrument aboard the SOHO satellite, Zhao has been examining a cluster of extraordinarily large sunspots in the same active region of the sun. He discovered that the dark orange-red spots of intense electromagnetic activity actually spin rapidly in a counterclockwise direction at the surface, while deep below their magnetically twisted roots spin in the opposite direction.
"The surprising complexity of what we've found will surely change people's ideas of the sun's behavior," Scherrer said.
But more than that, he said, when the causes of the newfound complexity inside the sun are resolved, scientists may be able to provide warning of magnetic storms to astronauts in space as well as power companies and radio transmitters on Earth.