November 26, 2009
Quiet time on the sun stalls aurora viewing
By Ned Rozell
It's a slow season for aurora watchers, due to an extra-long quiet period on the great aurora generator and all-around giver of life the sun.
"For two years we've been in an unusual, very low, extended solar minimum," said Dirk Lummerzheim, an aurora forecaster at the Geophysical Institute at the University of Alaska Fairbanks. "That has an effect on aurora because aurora activity follows solar activity. The aurora hasn't been too exciting lately."
Like the booms and busts of snowshoe hares, the numbers of both solar flares and sunspots (dark splotches on the sun) peak about every 11 years. On the other side of that peak is a crash, and the sun has bottomed out in sporadic activity since early 2008. The sun has gone more than two years without spewing a significant solar flare, and sunspot counts have also been very low. And sunspots are not great aurora indicators anyway.
"There's a statistical connection, but the appearance of a sunspot doesn't guarantee aurora," said Roger Smith, a space physicist and director of the Geophysical Institute. "It isn't the sunspots that cause aurora; it's irregularities in the solar wind that liberate energy for these beautiful optical displays."
Syun-Ichi Akasofu, an expert on the aurora and former director of both the Geophysical Institute and the International Arctic Research Center, agrees that people place too much emphasis on the connection between sunspots and aurora activity. He says the presence of another irregularity on the surface of the sun a large, cool area called a coronal hole often generates nice aurora for those in the north as emissions from the hole rotate toward Earth every 27 days or so.
According to Akasofu, we see more of the coronal hole type of aurora than people in the Lower 48. He says: "The stream from a coronal hole is weaker than a blast wave (caused by a solar flare.) Sightings of this type of aurora are confined to high latitudes, like Alaska. In Iowa, you won't see them."
Aurora sightings have been scarce in southern Alaska this year, and forecasts have been tepid at http://www.gedds.alaska.edu/AuroraForecast/.
"In Anchorage, it's very difficult to see aurora," Lummerzheim says. "In Fairbanks, it's not too bad. If you go to the Brooks Range, you get regular aurora, but we don't have that big (solar) storm that pushes the aurora south."
If you want to see aurora right now, at any cost, catch a flight to Barrow or Kaktovik, Lummerzheim says.
"On the northern coast of Alaska, we have aurora every day," he says. "It may be boring aurora, a weak green glow just over the horizon, but it's there."
But what goes down must go up, right? In the case of that awesome nuclear reactor in the sky, scientists look to the past activity as a possible predictor of what is to come. Except for a mysterious 70-year period without sunspots in the 17th century, solar cycles have lasted from about nine to 14 years from trough to trough, and the last bottoming out of solar activity was 13 years ago, in 1996.
"We don't understand the physics of the sun enough to make confident predictions," Lummerzheim says. "But the general consensus is that we're getting into the end of the minimum, and we expect (solar activity, and, perhaps, aurora sightings) to go up as winter progresses."
This column is provided as a public service by the Geophysical Institute, University of Alaska Fairbanks, in cooperation with the UAF research community. Ned Rozell is a science writer at the institute.
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