Paper#: 128
Poster #:
Session Name: Workshop 4B: Tail Instabilities
Room: 200ABC
Day: Tuesday
Time: 4:10-4:30 p.m.
Abstract Title: The Self-Organized Critical Plasma Sheet and Substorm Onset
PresentSurname: Klimas, A.J.
All Authors: A.J. Klimas, V. Uritsky, D. Vassiliadis, R.S. Weigel, D.N. Baker
Abstract : Our recent analysis of Polar UVI image data has now made the evidence for self-organized criticality (SOC) in the magnetospheric dynamics difficult to interpret in any other way. This analysis will be reviewed. The results support our earlier suggestion that this SOC component of the dynamics is centered in the plasma sheet and that it is related to the flow bursts and associated localized reconnections that have been observed there. It is necessary now to develop an interpretation of SOC in a plasma physical context. A plasma sheet model that may evolve into SOC will be discussed. The model contains a two-dimensional resistive MHD component coupled to a current driven instability that generates anomalous resistivity when and wherever the current density exceeds a critical threshold. In general terms, the model strongly couples fluid phenomena at MHD scales with phenomena at kinetic scales in an idealized manner. This strong coupling between such divergent scales introduces the possibility of multi-scale behavior in the intervening range of scales, and thus to the possibility of scale-free self-organized criticality. Numerical simulations of the plasma sheet model will be presented. The model exhibits quiet loading intervals interspersed with extremely dynamic unloading intervals during which magnetic flux is both annihilated and lost through plasmoid ejection. Based on the simulation results, a possible mechanism for the transition in the plasma sheet from sporadic localized reconnection to global organized reconnection at or near substorm onset will be discussed.