Magnetospheric substorms.

A proposed model of the substorm growth phase describes a gradual development of internal magnetospheric convection driven by enhanced field-line reconnection at the front-side magnetopause. The observed increased tail magnetic field, inward motion of the tail current system, and inward displacement of the plasma sheet inner edge are shown to follow from a line-tied inward motion of the dayside magnetopause and a slow development of magnetospheric convection. Resulting changes in the nightside auroral oval ionosphere lead to the formation of the auroral electrojet which is the ground signature (magnetically) of substorm breakup.