Cosmic Substorms and the Northern Lights

Back when I was in college, I took part in a research internship at the Indiana University Cyclotron Facility. Part of the work I was involved in pertained to bombarding satellite circuit boards with high-energy proton radiation so that they could test what happened to the boards under those conditions when they are exposed to the sort of charged particle radiation that they might encounter in space.

This same cosmic radiation - energetic streams of charged particles spewed forth from the sun - not only interferes with satellites, but also collides with our own atmosphere and magnetic field. Fortunately for all life on Earth, most of the radiation is deflected away from the Earth but some makes it through the Earth's protective outer shells ... and some results in the colorful displays known as the aurora borealis, or "northern lights."

An artistic rendition of the magnetic substorms
which cause the aurora borealis
NASA/THEMIS mission

In February 2007, NASA launched five satellites collectively called Time History of Events and Macroscale Interactions during Substorms (THEMIS) which measure the Earth's magnetic field interactions in response to the solar wind, at varying altitudes. Results from a February substorm have now been released in the journal Science, indicating that the substorms may provide several minutes warning - a great benefit in attempts to protect against their effects.

The charged particles, it seems, cause the Earth's magnetic field to bend, rip, and then suddenly rejoin, analogous to the snapping of an electromagnetic rubber band. The overload of energy is then directed back toward the Earth. This overall process is known as magnetic reconnection and has long been suspected as being involved in the formation of the auroras.

While accolades for the report seem solid, there is always the skeptical note of caution - this time presented by Los Alamos physicist Reiner Friedel, who points out that "if there's one thing we've learned about substorms over the past 40 years it's that no two are alike." In other words, taking these results and generalizing them into a statement about all substorms might be premature.

Having personally seen the northern lights, I can honestly say that they are one of the few wonders I've witnessed which I don't feel the need to explain or understand. They are a site to behold and value even without knowing the cause ...

... of course, if we can know the cause too, then that's even better.

Related Articles:

• NASA - THEMIS Satellites Discover What Triggers Eruptions of the Northern Lights
• Science Express - Shedding Light on Nighttime Brights
• Science - Tail Reconnection Triggering Substorm Onset (abstract,
• New Scientist - Magnetic slingshot creates auroras on Earth (includes some video images)
• Discover - Distant Turbulence in the Magnetic Field Triggers the Northern Lights
• Cosmic Ray Detector