Sky Lights

How to get the weather report for the northern lights

By Bob Berman|Sunday, April 01, 2001


Every 11 years or so, for reasons scientists have yet to fully comprehend, the sun comes a little undone. Magnetic storms rage across its surface, sunspots erupt like acne, and clouds of electrically charged particles fly outward at 2 million miles per hour. When those clouds reach Earth, they can overload power lines and disrupt communications, but they also have an oddly lyrical side: The rain of solar particles lights up the aurora, one of nature's most breathtaking spectacles.

Now is the perfect time to witness both the beauty and the beast. The current solar cycle apparently reached its maximum late last year. Auroras usually hit their peak the following year, so the view this month should be about as good as it gets. And these days, a fleet of spacecraft constantly monitors the sun's violent behavior and its earthly consequences. The results of these round-the-clock observations are available to anyone with an Internet connection— you just have to know where to look.

The SOHO satellite (sohowww.nascom.nasa.gov), launched in 1995, monitors the solar eruptions that unleash the energy of a billion atomic bombs in hours or less. For the past three years, the ACE spacecraft (www.srl.caltech.edu/ACE) has hovered a million miles sunward of Earth, measuring these blasts up to an hour before they reach us. Meanwhile, the year-old IMAGE satellite (pluto.space. swri.edu/IMAGE) generates global portraits of the subatomic particles from the sun as they crash into Earth's magnetic field. This information, combined with input from other, earlier satellites, enables researchers at the National Oceanic and Atmospheric Administration to produce plots of electrical activity (sec.noaa.gov/pmap) as readily as TV weathercasters track hurricanes.

Auroras light up Earth's poles as a solar storm sweeps by. The IMAGE satellite captures the swiftly changing glow.
Auroras light up Earth's poles as a solar storm sweeps by. The IMAGE satellite captures the swiftly changing glow.
Photo by Harald Frey, Stephen Mende/Space Sciences Laboratory/University of California at Berkeley

Early warnings from our space sentinels have helped us diminish the destructive impact of the sun's outbursts. On March 13, 1989, during the last solar maximum, a dazzling dusk-to-dawn light show over North America sparked electrical discharges that overloaded transformers and plunged Quebec into darkness. This time around, power companies know when to reroute current to compensate for solar-induced surges.

As an added bonus, IMAGE and its kin reveal where auroras are most active. When the charged particles from the sun reach Earth, some get trapped in our planet's magnetic field and reverberate between the poles, appearing in the IMAGE maps as doughnut-shaped zones of electrical activity around the Arctic and the Antarctic. Each aurora seen from the ground is a tiny segment of that enormous ring. Places like Fairbanks, Alaska, that sit right below the glowing doughnut enjoy overhead displays nearly every clear night. Down in the lower 48, auroras are much rarer but can look even more spectacular because they are usually seen from the side, a perspective that is often more majestic. The auroras may slowly unfold into luminous rays, blotches, arcs, lines, and curtains, or undergo split-second changes. Usually they are pale green, but occasionally the color plunges to deep bloodred.

With satellite readings available at the click of a mouse, you no longer have to guess blindly about the timing of solar eruptions and auroras. Today's Space Weather (sec.noaa.gov/today.html) issues three-day solar-storm forecasts and current photographs of the sun, while the SpaceWeather.com site presents a full report on current solar activity and is organized in an attractive format.

But the best way to catch glorious auroras is still persistence. Look to the north from time to time on clear, moonless nights. One sighting and you'll appreciate, in a way no satellite can capture, the subtle alchemy that turns solar turmoil into a wall of ghostly fire.







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