On nonlinear plasma instabilities during the substorm expansive phase onset

Abstract

Using a stability analysis based on a Lagrangian–Hamiltonian approach to magnetohydrodynamics, this paper addresses the stability of the Earth’s magnetotail during the later stages of the growth phase of the substorm. The analysis shows that the magnetotail at about 10–12RE is the likely region for instability. Furthermore, the analysis helps to explain why the substorm intensification begins on field line mapping from the Earthward edge of the substorm plasma sheet to auroral arcs near the equatorward edge of the auroral region. Our model and analysis provides a possible explanation for pseudobreakups as well as the initiation of more global substorm intensifications. A stability analysis of the evolving stretched field configurations of the growth phase shows that initially, at a certain level of stretching and in regions where the plasma β is 5–10, localized instabilities are possible. These localized instabilities saturate before producing a more global instability and the reconfiguration of the magnetic field topology of the magnetotail. Eventually the threshold for nonlinear instabilities is reached and a global, explosive instability is possible. Even though this paper looks only at the possibility of explosive instabilities and the initial stages of the substorm intensification, it provides an important first step in forming a complete picture of the substorm instabity and the subsequent return to a lower energy, metastable state through dipolarization of field lines in the magnetotail. A number of important features in the initiation of the substorm intensification can be explained by considering an explosive ballooning mode. Nevertheless, a more complete analysis of the plasma dynamics associated with the instability initiating the substorm intensification and the subsequent evolution of the substorm, including kinetic effects and reconnection, is needed for a more complete model of the substorm process.

Comment on “Tail Reconnection Triggering Substorm Onset”

“…2K). This sequence is in agreement with several previous studies and the inside-out model of substorm onset (4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15).…”

Behavior of substorm auroral arcs and Pi2 waves: implication for the kinetic ballooning instability

“…The NENL model asserts that the magnetic reconnection initiated outside 15 R E in the magnetotail produces fast bursty bulk plasma flows which arrive at the near-Earth region with flow braking to cause substorm onset (e.g., Angelopoulos et al, 1992;Shiokawa et al, 1998). The near-Earth onset model proposes that some instabilities are initiated in the near-Earth plasma sheet to cause substorm onset and subsequent expansion (e.g., Lui et al, 1991;Roux et al, 1991;Samson et al, 1992;Cheng and Lui, 1998;Lee et al, 1998;Cheng and Zaharia, 2004;Cheng, 2004;Dobias et al, 2004;Lui, 2004;Saito et al, 2008). In particular, the theoretical calculation of ballooning instability in the 3-D magnetospheric equilibrium that models the growth phase magnetosphere showed that the low-frequency instability in the Pi2 frequency range has the maximum growth rate in the strong cross-tail current region, and the most unstable ballooning mode field line region can be traced to the ionosphere in the transition region between the Region 1 and Region 2 currents (Cheng and Zaharia, 2004;Cheng, 2004).…”

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.…”