Authors

L. R. Lyons
Department of Atmospheric Sciences
University of California, Los Angeles
Los Angeles, CA 90095-1565

Paper based on invited presentation at Frontiers of Magnetospheric Plasma Physics Symposium held at ISAS in 2002
in Colloquium on Frontiers of Magnetospheric Plasma Physics Symposium, COSPAR publications, 2003 (in press).

Abstract

It is now know that there are several different types of auroral zone disturbances, each reflecting fundamentally different processes within the magnetosphere-ionosphere system. Four types known to be dynamically important are described here. Substorms follow a 0.5 hr growth period of enhanced convection. Onset occurs within the near-Earth plasma sheet and is often followed by new magnetic X-line in the mid-tail. Evidence now indicates that substorm onset results from a transition from a stable to unstable state of the nightside magnetosphere that initiates a few minutes prior to onset as the result of a reduction in the strength of convection caused by an appropriate change in the interplanetary magnetic field impacting the magnetosphere. Convection driven auroral enhancements occur at midnight-to-dawn MLTs and result from plasma sheet electrons, which are strongly energized during periods of enhanced convection and magnetic drift around the dawn side. Enhancements in solar with dynamic pressure cause global disturbances that can be quite dramatic. These disturbances consists of increases in magnetospheric and ionospheric currents and electric fields, enhancements in auroral emissions and broadening of the auroral oval, and significant shrinkage of the polar cap size. Poleward boundary intensifications (PBIs) are auroral enhancements that initiate along the poleward boundary of the auroral oval. They occur during all overall levels of geomagnetic activity and are associated with few minute flow bursts in the tail plasma sheet. They are the most common disturbance. They are often repetitive and may be a manifestation of a large-scale ULF oscillation.

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Paper (pdf format)