Characteristics of untriggered substorms

It is generally believed that most substorms have some kind of trigger such as a northward turn in the interplanetary magnetic field (IMF). We have identified over 200 isolated substorms in the North American sector from 1998-2002 based on the auroral electrojet index (AE). From this set of events, we have identified several that do not seem to have a solar wind trigger. In this presentation, we will discuss the characteristics of these events and contrast them to several events that seem to have a trigger.