COUPLED-MODE SCENARIO FOR THE MAGNETOSPHERIC DYNAMICS

Substorm phenomena are reviewed with emphasis on the magnetospheric so urce region of the onset, on the morphology of the initial breakup and subsequent activations, and on the variable character of individual s ubstorms. We provide evidence that before the substorm onset and durin g the following activations an intense, thin current sheet is formed a t the interface between the quasi-dipolar and taillike magnetic field regions. We infer that the initial breakup, the following multiple act ivations, pseudobreakups, and other short-term activations during nons ubstorm times are all similar in morphology and have the same formatio n mechanism. We postulate that the elementary units of energy dissipat ion, impulsive dissipation events, which are localized in space and ha ve a short lifetime of similar to 1 min, are the manifestations of tai l reconnection. We also emphasize the evidence that previous authors h ave presented in favor of this time dependence and localization. On th e basis of the above, we suggest that there are two basic magnetospher ic processes responsible for energy storage and dissipation during bot h substorm and nonsubstorm times: A global and slow quasi-static tail reconfiguration responsible for the energy storage, and a sequence of local, sporadic, short-term energy dissipation events. These competiti ve processes can be observed most the time in some part of the plasma sheet; their relative intensity determines the type of large-scale dyn amic evolution. In this scenario, the various dynamical situations are interpreted as variations in the balance between the two competing pr ocesses.