By MARY PEMBERTON
The Associated Press
ANCHORAGE, Alaska -- A Web site is taking some of the guesswork out of when to make a Thermos of hot coffee, throw on a scarf and venture out into the cold night to take in the northern lights -- even if you're far away from the aurora epicenter in Alaska.
The Geophysical Institute at the University of Alaska Fairbanks has revamped its Web site for aurora borealis watchers. The improved site offers interactive world maps and three forecasts: daily, extended and long-term.
"This is one, if not the most, visited Web sites we have," said Dirk Lummerzheim, a professor of the upper atmosphere at the institute, who helped revamp the Web site.
The site is accessible at www.gedds.alaska.edu/AuroraForecast.
It's not difficult to see the northern lights in Alaska's second-largest city: Fairbanks averages about 243 nights a year of auroral activity. Only 360 miles to the south, Anchorage gets about 30 good nights a year.
"The probability of seeing aurora in Fairbanks is ridiculously high," Lummerzheim said.
But the Web site also could be a valuable tool for those in the Lower 48, where sightings are far less frequent but do occur.
New York and Chicago get about 10 nights of aurora activity a year, Seattle between five and 10 nights, and New Orleans and San Francisco about one glimpse of the aurora each year. Even Cuba gets the occasional display -- about once every 10 years.
The trick is going out when there is going to be a really good light show -- on the horizon in the Lower 48, or if in Alaska, the kind of display where green and red lights arc, swirl and dance overhead in awe-inspiring displays.
That's where the institute's revamped Web site comes in.
The site was popular even before getting a new look in August, receiving about 20,000 hits a month during the fall and winter aurora-viewing season. Charles Deehr, the institute's professor emeritus of physics, expects the Web site to draw even more interest now.
That's because the site is interactive, providing users from around the world with five different maps to choose from: Alaska, North America, Europe, North Polar and South Polar. Once a user calls up one of those maps, the Web site pulls that map up again automatically the next time that user logs on.
The maps show a swath of green where the aurora borealis is active. In bold, black letters in boxes of different colors signifying auroral activity are the one-hour forecasts: green for quiet, yellow for medium and red for active.
Deehr, 70, has been preparing the forecasts for more than a decade.
The one-hour and 28-day forecasts are done automatically. The three- to five-day forecast is more complicated, requiring hands-on forecasting.
"We make one for each day where we take everything into account that we can take into account," Deehr said.
The one-hour forecast is pretty easy to figure out, Lummerzheim said. That's because the U.S. has a satellite stationed between the sun and the Earth where it measures the solar wind while it is about an hour away from Earth.
"The wind that comes from the sun makes the aurora. It passes this satellite one hour away from Earth," Deehr said. "It is the condition of the solar wind that determines what kind of aurora there is going to be, how active it is going to be."
Deehr said the one-hour forecast is reliable.
"You can sit inside and watch the one-hour forecast and know what it is going to be like. If it says 'quiet' and it is 3 o'clock in the morning, go to bed," he said.
The best time normally for watching the aurora is between 10 p.m. and 2 a.m.
The 28-day forecast is a rough projection that draws on past data and relies on a 28-day solar rotation cycle.
To do the three- to five-day forecast, scientists start by looking at the sun and the solar wind.
"We can look ahead and see changes in the solar wind coming down the line that we can interpret," Deehr said.
The solar wind of magnetic and particle components blows all the time, Deehr said. It is the changes in the wind that produce the aurora. For example, solar flares produce distortions in the solar wind.
"What happens is that the sun's magnetic field hooks up with the earth's magnetic field and starts the generator that is produced by particles flowing past the earth," Deehr said. "It is a huge generator and it generates thousands of volts of electricity in the magnetic field of the earth. That leads to the aurora."
The electricity glowing in the earth's atmosphere is the aurora, Deehr said.
"The whole thing is driven by the solar wind interacting with the earth's magnetic field," he said.
About 11,000 users have signed up for the Web site's Aurora Alert service. It tells users when a really good display is likely to occur. The Web site also offers aurora watchers a forum to talk back and forth or ask questions of the scientists.
"There is a lot of interaction," Deehr said, noting that some enthusiasts "come back all the time."
The Geophysical Institute doesn't track how many Web users are from outside Alaska, but Kathy Bertram, the education outreach director, suspects it's quite a few since they get so many calls from people elsewhere.
The Lower 48 calls usually come after people have seen the northern lights on the horizon. The international calls flood in as people plan vacations to Alaska and want to know the forecast for aurora activity during their visit.
"They want to predict three months in the future, but they understand they have a better chance of seeing it here than where they are," Bertram said.
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