Nonlinear stability of the near-Earth plasma sheet during substorms: 9 February 1995 event

Abstract

It has been previously demonstrated that several minutes prior to an onset of a magnetospheric substorm the near-Earth plasma sheet becomes unstable to resonance-type perturbations. The next logical step, examined here, is an assumption that the velocity shear in the resonance would lead to a development of a Kelvin–Helmholtz (KH) instability. Using a Grad-Shafranov equilibrium constrained by CANOPUS data, we analyze the stability properties of the near-Earth plasma sheet in the presence of a field-line resonance-generated KH instability at around 10 Earth radii. The results of the analysis are in general agreement with observations and computer modeling of substorms. As a part of the analysis, we discuss the importance of the proper distinction between the stability properties of the magnetotail, and the trigger mechanism responsible for the instability. While these two aspects of a substorm may be (and likely are) related, it is possible that they involve different types of processes that work in a complementary fashion. PACS Nos.: 06.54, 27.40, 27.72, 27.88

Obliquely propagating electromagnetic drift ion cyclotron instability

“…Various plasma instabilities have been proposed as playing important roles during the substorm onset process. These include the tearing [Schindler, 1974;Sitnov et al, 1997;Zelenyi et al, 2008], ballooning [Cheng and Lui, 1998;Bhattacharjee et al, 1998;Dobias et al, 2004;Zhu et al, 2003;Saito et al, 2008;Friedrich et al, 2001], lower hybrid drift [Shinohara et al, 1998;Yoon et al, 2002;Mok et al, 2006], Kelvin-Helmholtz [Rostoker and Samson, 1984;Dobias et al, 2006], and the ion Weibel [Yoon and Lui, 1993;Sadovskii and Galeev, 2001] instabilities.…”

Intermittency of storms and substorms: is it related to the critical behaviour?

“…Our results suggest that if one seeks a trigger then one will tend to find many different possible sources of a substorm onset; it is not the trigger that is so important as the energetic state of the high-latitude magnetosphere. Dobias et al (2004Dobias et al ( , 2007 demonstrated that during the growth phase there is a significant reconfiguration of the free energy in the near-Earth plasma sheet. Using an assumption of FLR-like perturbations present in the system just prior to the onset, they demonstrated that the plasma sheet becomes explosively unstable at the time of the onset.…”