A kinetic ballooning/interchange instability in the magnetotail

Abstract

[1] Three-dimensional electromagnetic particle-in-cell simulations are used to investigate the stability properties of a plasma sheet equilibrium with a minimum in the magnetic normal (B z ) component. Such a configuration is found to be unstable to a ballooning/ interchange type mode that is localized tailward of the B z minimum. The mode has a relatively short dawn-dusk wavelength of the order of the ion Larmor radius in the B z field (∼2000 km) and a phase velocity in the direction of the ion diamagnetic drift with a magnitude about one-fifth of the drift speed. The real frequency is about 60% of the midplane ion cyclotron frequency. The dominant mode polarization is d and dB k . A linear kinetic analysis including bounce and drift resonance interactions for the electrons and an orbit average over the flux tube volume for the Boltzmann term in the ion density perturbation produces agreement with the simulation mode properties and permits identification of the mode as the low-frequency extension of the lower hybrid drift instability in straight magnetic geometry. In its nonlinear evolution, the mode develops Rayleigh-Taylor fingers that extend across the B z minimum and into the near-Earth dipole region. These fingers transport magnetic flux earthward, and the flux is redistributed by electron Hall currents that flow around the fingers. This mode is likely to contribute to the nearly continuous presence of turbulence in the center of the plasma sheet.

Non-triggered auroral substorms and long-period (1–4 mHz) geomagnetic and auroral luminosity pulsations in the polar cap

“…Panov et al (2012) observed "strong magnetic oscillations with period from 20 to 100 s" in the plasma sheet a few tens of minutes before the breakup using THEMIS data. The authors concluded that these measurements partly confirm the mechanism of the development of a kinetic ballooning or interchange instability mentioned by Pritchett and Coroniti (2010). Golovchanskaya et al (2015) assumed that Pi2 and Pc5 pulsations, associated with substorms, might be interpreted as a signature of the ballooningtype perturbations in the magnetotail.…”

Statistical visualization of the Earth's magnetotail and the implied mechanism of substorm triggering based on superposed-epoch analysis of THEMIS data

“…Sitnov and Schindler, 2010), ballooning/interchange instabilities (e.g. Pritchett and Coroniti, 2010) or kink-type instabilities (Erkaev et al, 2008) may be involved in this relaxation process. The relaxation of the catapult current sheet produces fast convective earthward flows, and this leads to considerable perturbations to the instability which already developed in the inner region.…”

Structure, force balance, and evolution of incompressible cross-tail current sheet thinning

“…A similar scenario emphasizing the role of the high beta on closed field lines has also been suggested for solar flares [Shibasaki, 2003]. The stability of 2D (x, z) magnetotail in a high beta plasma has been examined both theoretically and numerically by various authors studying the ballooning instability [e.g., Miura et al, 1989;Lee and Wolf, 1992;Hurricane, 1997;Pu et al, 1997;Bhattacharjee et al, 1998;Cheng and Lui, 1998;Horton et al, 2001;Zhu et al, 2007;Pritchett and Coroniti, 2010;Raeder et al, 2010] and also the tearing instability [Sitnov and Schindler, 2010]. Collisionless plasmas in inhomogeneous magnetic fields are subject to various kinetic effects such as bounce motion of particles.…”