The “driving engine” of auroral substorms is rather far out in the magnetotail and then propagates inward, a recent study suggests. The results are based on test particle simulations of dispersionless particle injections and indicate an origin distance of more than 15 Earth radii (RE) away (1 RE = 6380 kilometer). The work is also showing how such dispersionless injections can, in principal, be produced.
Dispersionless particle injection is one of the characteristic features of substorm onset and refers to the sudden appearance of energetic ions and electrons over a broad range of energies (tens to hundreds of keV) in the Earth's magnetosphere. Such injection events are often seen near midnight on satellites in geosynchronous orbit in association with substorm onset.