Hi Eric,

That's a good question to ask.

The reason why auroras generally form near the Earth's north and south magnetic poles is related to the structure of the Earth's magnetic field and the electrical currents that flow throughout the Earth's magnetosphere. If you look at a satellite photo of the aurora, you will notice that the auroras do not form right at the magnetic poles. Instead, the auroras actually occur in a ring, called the auroral oval, that encircles the poles. If you start near the Earth's surface, at the foot of the magnetic field lines that pass through the night side auroral oval, and follow along these magnetic field lines away from the Earth, you will end up in a region of the magnetosphere that scientists call the plasma sheet. The plasma sheet happens to be located in the inner part of a region called the magnetotail. When the solar wind interacts with the day side of the Earth's magnetosphere, the energy transfered from the solar wind to the magnetosphere eventually convects to the night side, where it is stored in the Earth's magnetotail. Through a series of complicated processes that are not completely understood, the energy stored in the magnetotail can be explosively released, causing a reconfiguration of the magnetic field. When this happens, particles in the plasma sheet are accelerated to high speeds and the huge electrical currents that power the aurora are generated. Scientists call this a substorm.

Kris