Home Articles Facts Games Poems & Quotes
The Sun Goes Haywire

Solar maximum is years past, yet the sun has been remarkably active lately. Is the sunspot cycle broken?

by Dr Tony Phillips

Imagine you're in California. It's July, the middle of summer. The sun rises early; bright rays warm the ground. It's a great day to be outside. Then, suddenly, it begins to snow - not just a little flurry, but a swirling blizzard that doesn't stop for two weeks.

That's what forecasters call unseasonal weather.

It sounds incredible, but "something like that just happened on the sun," says David Hathaway, a solar physicist at NASA's Marshall Space Flight Center.

Only a few weeks ago solar activity was low. The face of the sun was nearly blank - "very few sunspots," says Hathaway - and space weather near Earth was mild. "Mild is just what we expect at this point in the 11-year solar cycle," he explains. "The most recent maximum was in 2001, and solar activity has been declining ever since."

Sunspots cause solar flares and, usually, the biggest flares come from the biggest spots. The three giant sunspots unleashed eleven X-class flares in only fourteen days - equaling the total number observed during the previous twelve months. "This was a big surprise," says Hathaway.

The effects on Earth were many: Radio blackouts disrupted communications. Solar protons penetrated Earth's upper atmosphere, exposing astronauts and some air travelers to radiation doses equal to a medical chest X-ray. Auroras appeared all over the world - in Florida, Texas, Australia and many other places where they are seldom seen.

Researchers rank solar flares according to their x-ray power output. C-flares are the weakest. M-flares are middling-strong. X-flares are the most powerful. Each category has subdivisions: e.g., X1, X2, X3 and so on. A typical X-flare registers X1 or X2. On Nov. 4th, sunspot 486 unleashed an X28 flare - the most powerful ever recorded.

"In 1989 a flare about half that strong caused a widespread power blackout in Quebec," recalls Hathaway. The blasts of a fortnight ago were aimed away from Earth, so its effects on our planet were slight - a bit of good luck.


An extreme-ultraviolet telescope onboard the orbiting Solar and Heliospheric Observatory (SOHO) captured this false-color movie of the Nov. 4, 2003, X28 superflare near the sun's limb

All this happened two years after solar maximum, which raises a question: is something wrong with the solar cycle? Is the sun going haywire?

"Nothing's wrong," reassures Hathaway. The sun isn't about to explode, nor is the sunspot cycle broken. "These latest sunspots were whoppers," he allows, "but sunspot counts averaged over many weeks are still declining as predicted. We're still on course for a solar minimum in 2006."

Indeed, it's possible that what we've just experienced is a normal part of the solar cycle, speculates Hathaway. "There's a curious tendency for the biggest flares to occur after solar maximum - on the downslope toward solar minimum. This has happened during two of the last three solar cycles." The plot below illustrates his point.

Consider the year 1984, says Hathaway. Sunspot counts were plunging, and the sun was rapidly approaching the 1985-86 solar minimum. Suddenly a giant sunspot appeared, Jupiter-sized like sunspot 486, and unleashed two dozen M-flares and three X-flares, including a remarkable flare registering X13. People then probably wondered too if the solar cycle was broken.

"It's hard to be sure what's normal and what's not," notes Hathaway. "Astronomers have been observing x-rays from the sun for only 35 years - or three solar cycles. We can't draw good statistical conclusions from so few data."

Using data archived by NOAA's Space Environment Center, Francis Reddy created this plot of sunspot number and X-class solar flares during the last three solar cycles.

One thing is certain, though: flurries of solar activity can happen at any time. The next time, says Hathaway, could be close.

Sunspot 486 and its companions are on the far side of the sun now, carried around by the sun's 27-day rotation. "We suspect they're still active," says Hathaway, because the Solar and Heliospheric Observatory - a sun-watching satellite - has photographed clouds of gas being thrown over the sun's limb by unseen explosions.

And then...? No one knows. "We might get some more unseasonal space weather," says Hathaway. But this time he won't be surprised.


Home   l  Biology   l  Physics   l  Planetary Science   l  Technology   l  Space

First Science 2014