A new model for auroral breakup during substorms.

A model for substorm breakup is developed, based on 1. the relaxation of stretched (closed) dipolar field lines, and 2. the formation of an incipient current wedge within a single arc structure. It is argued that the establishment of a coupled current structure within a single arc leads to a quasi-stable system; i.e., the pre-breakup regime. Perturbation of the pre-breakup structure leads to an instability criterion.