Researchers on the Themis (Time History of Events and Macroscale Interactions during Substorms) mission say they’ve used a quintet of satellites around the Earth to monitor the Northern Lights phenomenon from start to completion and can definitively explain it.
“The Earth is bathed in the solar wind which carries with it the magnetic field of the Sun,” explained Nicola Fox, a Johns Hopkins University scientist.
“The field can be in many directions but when it opposes Earth’s magnetic field, just like two opposite poles of a magnet will attract, the two field lines will break and join together. This reconnection allows vast amounts of solar energy to enter into our own magnetosphere, generating a substorm which culminates in the formation of aurora.”
Observations from Themis show that a substorm starts to occur in a area of space one third of the way to the Moon and exhibits a particular pattern. The pattern consists of a period of “reconnection”, followed by rapid auroral brightening and rapid expansion of the aurora towards the Earth’s poles. This culminates in a redistribution of the electrical currents flowing in space around Earth.
Interesting tidbit: the magnetic flux lines around the earth’s pole is roughly equivalent to a 30,000 volt battery in space and can generate 650,000 Amps of current into the arctic.