November 12, 2003: 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."
Then, suddenly, in late October the sun began to behave strangely. Three giant sunspots appeared, each one larger than the planet Jupiter.
In California where smoke from wildfires dimmed the sun enough to look straight at it, casual sky watchers were startled by the huge blotches on the sun. One of them, named "sunspot 486," was the biggest in 13 years.
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. Last week's blast was aimed away from Earth, so its effects on our planet were slight - a bit of good luck.
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.
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