Stability of the Magnetotail Current Sheet With Normal Magnetic Field and Field-Aligned Plasma Flows

One of the most important problems of magnetotail dynamics is the substorm onset and the related instability of the magneotail current sheet. Since the simplest 2D current sheet configuration with monotonic Bz was proven to be stable to the tearing mode, the focus of the instability investigation moved to more specific configurations, for example, kinetic current sheets with strong transient ion currents and current sheets with non-monotonic Bz (local Bz minima or/and peaks). The stability of the latter current sheet configuration has been studied both within kinetic and fluid approaches, whereas the investigation of the transient ion effects was limited to kinetic models only. This paper aims to provide a detailed analysis of the stability of a multi-fluid current sheet configuration that mimics current sheets with transient ions. Using the system with two field-aligned ion flows that mimic the effect of pressure non-gyrotropy, we construct a 1D current sheet with a finite Bz. This model describes well recent findings of very thin intense magnetotail current sheets. The stability analysis of this two-ion model confirms the stabilizing effect of finite Bz and shows that the most stable current sheet is the one with exactly counter-streaming ion flows and zero net flow. Such field-aligned flows may substitute the contribution of the pressure tensor nongyrotropy to the stress balance but cannot overtake the stabilizing effect of Bz. Obtained results are discussed in the context of magnetotail dynamical models and spacecraft observations.

Automated summary

The paper provides a detailed analysis of the stability of a multi-fluid current sheet configuration that mimics current sheets with transient ions in the magnetotail dynamics. It discusses the stabilizing effect of a finite Bz on current sheet stability, with counter-streaming ion flows and zero net flow being identified as the most stable configuration. The findings are important for understanding magnetotail dynamical models and spacecraft observations.