Self-organized criticality in the substorm phenomenon and its relation to localized reconnection in the magnetospheric plasma sheet

Evidence is presented that suggests that there is a significant self-organi zed criticality (SOC) component in the dynamics of substorms in the magneto sphere. We assume that observations of bursty bulk flows, fast flows, local ized dipolarizations, plasma turbulence, etc, show that multiple localized reconnection sites provide the basic avalanche phenomenon in the establishm ent of SOC in the plasma sheet. First results are presented from a study of this avalanche process based on this working assumption. A magnetic field reversal model is discussed. Resistivity, in this model, is self-consistent ly generated in response to the excitation of an idealized current-driven i nstability. When forced by convection of magnetic flux into the field rever sal region, the model yields rapid magnetic field annihilation through a dy namic behavior that is shown to exhibit many of the characteristics of SOC. Over a large range of forcing strengths, the annihilation rate is shown to self-adjust to balance the rate at which flux is convected into the revers al region. Several analogies to magnetotail dynamics are discussed: (1) It is shown that the presence of a localized criticality in the model produces a remarkable stability in the global configuration of the field reversal w hile simultaneously exciting extraordinarily dynamic internal evolution. (2 ) Under steady forcing it is shown that a loading-unloading cycle may arise that, as a consequence of the global stability, is quasi-periodic and, the refore, predictable despite the presence of internal turbulence in the fiel d distribution. indeed, it is shown that the global loading-unloading cycle is a consequence of the internal turbulence. (3) It is shown that under st eady, strong forcing the loading-unloading cycle vanishes. Instead, a recov ery from a single unloading persists indefinitely. The field reversal is gl obally very steady while internally it is very dynamic as field annihilatio n goes on at the rate necessary to match the strong forcing. From this resu lt we speculate that steady magnetospheric convection events result when th e plasma sheet has been driven close to criticality over an extended spatia l domain. During these events we would expect to find localized reconnectio n sites distributed over the spatial domain of near criticality, and we wou ld expect to find plasma sheet transport in that domain to be closely relat ed to that of BBF and fast flow events.