What is a magnetospheric substorm

The paper suggests that if the solar wind-magnetosphere energy coupling increases above about 10 to the 18th erg/sec, the magnetosphere suddenly develops a more efficient energy dissipation process than that operating during periods of less than 10 to the 18th erg/sec. Discussion covers the appearance 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.