By Jenny Neyman
What was forecast to be the most active aurora display so far this fall and winter Monday night was shrouded by overcast skies on the central Kenai Peninsula. But sky watchers can take heart — this performance might have been missed, but the show is far from over.
“We have just passed the peak of the current 11-year cycle, and are on the waning side. Studies have shown that this tends to be the time of the most active aurora here on Earth, though the exact mechanisms are not fully understood,” said Don Hampton, research assistant professor with the University of Alaska Fairbanks Geophysical Institute.
The aurora is driven mostly by solar wind — a stream of charged particles constantly boiling away from the sun, Hampton said.
“Think of the steam off a cup of coffee or tea,” he said. “There is a cycle in how the sun produces this stream, based on an 11-year flipping back and forth of the sun’s internal magnetic field. When it is in the process of flipping back and forth, it can increase the production of sunspots.”
Sunspots release the charged particles in a burst, rather than a steady stream. When that burst reaches Earth it creates a much more active aurora. The burst of particles from the solar storms come off the sun at 1 to 2 million kilometers per hour and take about 75 to 150 hours to travel the 150 million kilometers to Earth. Ground-based telescopes track solar storms from Earth, and aurora forecasters refine their predictions with spacecraft that sit about 1 million kilometers away from Earth toward the sun.
“When we see the solar wind arrive there we have about one to two hours to get ready to observe the excitement,” Hampton said.
That’s how the Geophysical Institute can provide daily aurora forecasts for multiple days in advance, as well as hourly predictions.
Geomagnetic storms on the sun are rated in intensity from minor G1 to extreme G5. For comparison, a G1 storm is likely to happen 900 days per 11-year cycle, while a G5 only happens four days every 11 years.
A strong, G3-level storm happens about 130 days per 11 years and can cause some impressive aurora activity. Just such a storm was brewing Monday, resulting in a “High + +” aurora activity forecast for Monday night — rated a seven on a zero to nine scale.
The aurora was expected to be active overhead as far south as Wyoming, Nebraska, Missouri and New York, and visible low on the horizon as far south as Nevada, Oklahoma and North Carolina.
In Alaska, the central Kenai Peninsula should have been set for a prime display — if the clouds weren’t in the way.
But the aurora has already been quite active this year — though in Alaska we only get to see it when it gets dark enough at night — and should continue to be so until summer at northern latitudes once again banishes nighttime darkness.
Statistically, the equinox months of September and March are best for aurora activity, but it’s only a small bump in activity, Hampton said. There are better times of night to view, though. In general, the higher the latitude, the earlier in the evening aurora activity will likely escalate.
“The most likely time to see the most active aurora is around what is called ‘magnetic midnight.’ That is when the magnetic pole and lies between us and the sun,” Hampton said.
In Fairbanks, the best viewing tends to be between 1:30 to 2 a.m., he said, which would be about the same on the Kenai Peninsula.
But, ultimately, the most important factor in viewing the aurora is clear skies. So keep an eye on the local weather forecast, as well as the aurora forecast.
The Geophysical Institute forecasts the aurora to be active (four out of nine) Wednesday, Thursday and Friday, and moderate (three out of nine) Saturday and Sunday. Weather forecasts are calling for a chance of clearing skies Wednesday night, Friday and Saturday.
For more aurora predictions, visit the Geophysical Institute at www.gi.alaska.edu/Aurora Forecast.