Substorm detonation

The rapid, Alfvenic timescale of "onset" has been an enigma ever since magn etospheric substorms were first identified. Investigators have proposed a v ariety of trigger mechanisms in an effort to account for the abrupt reconfi guration observed. No one mechanism clearly stands out as the single cause of substorms. Recent analysis has demonstrated that field lines in the tail of the magnetosphere are metastable to ballooning type instabilities via a process called "nonlinear magnetohydrodynamic detonation." Furthermore, th e perturbation amplitude necessary to activate the nonlinear instability is not large. Thus a variety of external and internal perturbations can trigg er the same basic nonlinear instability. The evidence for detonation as a m edium for the unification of substorm triggers is discussed.