Solar storms: Two breakthroughs could lead to better warnings
The solar storms that cause blackouts and damage satelites have always been hard to predict, but two new methods of monitoring them could lead to much more accurate forecasts.
(Page 2 of 2)
Subscribe Today to the Monitor
To spot the changes inside the sun that appear to herald a coming blossom of sunspots, a team led by Stanford University graduate student Stathis Ilonidis used data from the SOHO spacecraft, a collaboration between the European Space Agency and NASA. SOHO orbits the sun within a gravitational sweet spot that lies some 1.5 million miles from Earth, in the sun's direction. There, gravity from the sun and Earth in effect cancel each other, allowing the craft to stay put with few or no additional maneuvers needed.
Mr. Ilonidis and colleagues used an imager on SOHO that can detect changes in the intensity and direction of acoustic waves in the sun. These waves are generated by vigorous convection as the searing gases within the sun rise, cool, and sink again to be reheated by the star's nuclear furnace.
Scientists had long thought that the magnetic activity that generated sunspot regions originated deep within the sun. The results Ilonidis and colleagues are publishing in Friday's issue of the journal Science represent what he says are the first observations of this deep process.
The team looked at four different sunspot outbreaks and spotted the deep magnetic precursors for each. The strongest of their examples occurred Oct. 26, 2003. The next step is to look at a large number of sunspot outbreaks to see how consistently the precursor signals the team identified show up.
In addition to the Paul Revere-like "sunspots are coming" data SOHO provide, the team also says it's possible to estimate the intensity of a sunspot outbreak from the speed with which the magnetic fields responsible migrate up from deep in the sun.
Once an active region spawns a coronal-mass ejection, observations pioneered by Dr. DeForest's team could take over. The team used visible images from one of NASA's two STEREO spacecraft. The STEREO mission involves a pair of sun-watching orbiters traveling in opposite directions around the star but at the same distance as Earth.
Using new signal-processing techniques, the team was able to catch the full trip and evolution of a coronal-mass ejection by capturing the vanishingly faint sunlight that in effect glints off of the particles themselves.
Early in its travels, the massive cloud is dense and relatively compact, making it easy to see. But after it travels about 20 percent of the distance from the sun to Earth the cloud grows diffuse. By the time it reaches Earth three days later, it can arrive "as a 50-million-mile-tall wall of plasma," DeForest says.
As it travels, the plasma's interaction with the sun's extended magnetic field alters the cloud's shape and creates voids, filaments, and other features that make it increasingly difficult to detect.
DeForest's team used innovative image-processing techniques to tease out the light from the cloud. By the time the cloud reaches Earth, the light it reflects is about 10 billion times fainter than the light of a full moon, and some 10,000 times fainter than the stars within the spacecraft's field of view, but because of the way they processed the images they were able to see it.
The team, which described its research during a press briefing today, formally published its results recently in the Astrophysical Journal.