What is a magnetospheric substorm

It is suggested that if the solar wind-magnetosphere energy coupling, epsilon, increases above about 1018 erg/sec, the magnetosphere suddenly develops a more efficient energy dissipation process than that operating during periods of epsilon < 1018 erg/sec. It appears that the magnetosphere achieves this enhanced energy dissipation by interrupting the cross-tail current in the magnetotail and diverting it into the ionosphere, causing an enhanced Joule heat production in the ionosphere. The good correlation between epsilon and the total energy dissipated in the magnetosphere suggests that the substorm is more like a process directly driven by the solar wind, rather than an unloading process of energy accumulated prior to the onset. (Auth.)