Aurora Weather

I got word recently that a new building on the Poker Flat Research Range is being christened for Neil Davis, who served as first director for the range and who---sometimes by using imaginative and unorthodox methods---was chiefly responsible for creating the facility. I helped with public information during those early days, and grew to appreciate Davis' skill at explaining things clearly (that is, when he had time to explain things at all).

It's harder for me to catch the now retired Professor Emeritus Davis these days to ask for explanations, but fortunately he's taken up writing books to keep himself busy. The books have an adequacy of explanations, and sometimes even describe problems in need of explanation. For example, in The Aurora Watcher's Handbook, Davis devotes a short chapter to the connection between aurora and weather.

When you hear old-time Northerners comment, "Great weather for the aurora tonight," they are actually reporting on viewing conditions. Everybody who lives in the auroral zone soon learns that one sees more aurora when the weather turns cold. That's true from the first crisp night of autumn to the last blast of bitter chill in spring. But consider: cold weather is likely to be clear weather. That's not true for summer, but in summer the sky is too bright for aurora to be visible. In fact, scientists' instruments show that aurora goes on above thick clouds and during bright summer nights just as surely as it does during the clear, cold evenings we think appropriate for northern lights.

The weather connection that ought to be there comes about because both auroras and all manifestations of earthly climate have their ultimate source in the sun. It's not the same kind of solar energy that produces both effects, though. The sunlight that drives our planet's atmospheric engine reaches us eight minutes after it leaves the sun's surface. Assuming they escape from the sun at the same time, the electrically charged particles that generate auroras arrive a day or more later. This aurora-producing solar wind is not only slower than sunlight, it's also far weaker. Sunlight packs about 100 times the energy of the solar wind.

Sunspots link some manifestations of both weather and aurora, in a way that runs counter to old northern wisdom. Periods of few or no sunspots can be accompanied on Earth by colder weather and fewer auroras than usual. (The Maunder Minimum, the well-studied period from 1645 to 1715, was such a time.) it's easy to see how turmoil on the sun's surface, as shown by sunspots, could lead to more particles fleeing earthward to produce auroras. It's not so easy to see how many dark, cool sunspots could signify a solar surface hotter than usual, yet that's apparently how the sun works.

But the interesting and unresolved question is, Does the aurora affect the weather somehow? Davis comments on one study that seemed to show such an effect. Researchers found that storms beginning over the North Pacific during times of major auroral displays tended to grow more than did storms beginning at other times. It's also known that auroral processes affect both electric fields and air temperatures high above the ground, and those changes could reach down into weather systems.

Davis puts the possibility very neatly. Since auroral energies are relatively minor compared to those driving primary weather processes, "nothing more than a tickling of other processes seems possible. But a tickling of a dog's foot can lead to frantic activity, and the atmosphere's weather-making processes might behave likewise."

There are definite advantages to having Davis' explanations in a book. One can review as often as necessary without annoying the expert, for one thing. Then too, when I worked for Poker Flat, Davis did fire me. Several times.