Theory for the electron precipitation and current system that produces a magnetospheric substorm

It is found that the electron precipitation during a magnetospheric substor m can be attributed to particle scattering into the loss cone by the cyclot ron maser instability, where the resulting current system produces the acco mpanying dipolarization of the Earth's magnetic field. This model for a sub storm thereby explains substorm expansion, and predicts that the incoming e lectron precipitation during a substorm has to be the actual cause of a mag netospheric substorm. (C) 2001 American Institute of Physics.