Given the sheer power of this week's solar flares—and NASA's warning of a potentially severe geomagnetic storm, with potential disruptions of power grids, GPS, and communications—the sun storm striking us Thursday has been surprisingly soft.
And for good reason, solar physicist Alex Young explains.
Though scientists say the storm may still intensify as Friday approaches, the storm level is still at the G1 level—"minor" on the space-weather scale.
"At that level, the effects will be fairly minimal," said Young, of NASA's Goddard Space Flight Center. "Nothing that would actually cause any problems."
The solar storm's gentler-than-expected treatment of Earth so far has a lot to do with the direction the storm was traveling when it hit our planet's magnetic field, explained Young, who works on the Solar and Heliospheric Observatory project.
"The Earth's magnetic field has a northward direction to it," he said. There's also a magnetic direction to each solar storm, or coronal mass ejection (CME)—a burst of charged solar particles expelled from the sun the sun by the "snapping" of magnetic fields.
If, as with the current sun storm, a CME's magnetic field points northward, its interaction with Earth's magnetic field can be weakened—"the two are both pointed in the same direction," Young said.
"But if they're opposite each other—if the [storm's] magnetic field is southward—then there's a much stronger interaction. It allows much more energy to be pumped into Earth's magnetosphere."
Stronger Solar Storms to Come?
Despite today's less-than-apocalyptic showing, we're not totally in the clear, Young said.
The outbursts that spark CMEs typically occur at sunspots, magnetically turbulent regions that look dark because they're relatively cool, compared with the surrounding region—6,000ºF (3,300ºC) versus 10,000ºF (5,500ºC).
As the sunspot region that produced Wednesday morning's flares moves along the face of the sun, it's growing in complexity, increasing the chance for another Earth-oriented eruption.
"It's interesting, [sunspots] kind of look like a mole," Young said.
"And when you monitor a mole, they tell you, as long as it stays in a nice symmetric shape and it doesn't become really complicated and complex, it's OK.
"It's the same sort of thing with sunspots. ... When they become complicated and twisted, then that means the magnetic fields inside of them have become more twisted, like a rubber band twisting around until little knots pop up in it.
"Right now we have been monitoring that sunspot, and it is getting more complex," he added. "What that tells us is there is still the strong possibility of another X-class flare."
(See "The Sun: Living With a Stormy Star" in National Geographic magazine.)
X-class flares are the strongest types of solar flares, which are associated with CMEs.
At 5.4, the stronger of the two large March 6 flares was right in the middle of the X-class scale. This makes the larger flare the second strongest of the current, 11-year solar cycle, after an X6.9 on August 9, 2011.
The following flare, at X1.3, was roughly a fifth as strong as its partner.
Since the solar maximum, when the sun is at its most active, isn't expected to peak until 2013, we could see much stronger sun storm over the next year or so.
"This is part of the normal cycle," Young said.
"We will see probably bigger events, and they may or may not have a huge impact, but that's why NASA and NOAA and all these other agencies are monitoring it—so we can better understand it."