Structure and consequences of the kinetic ballooning/interchange instability in the magnetotail

The structure and dynamical consequences of the kinetic ballooning/interchange instability (BICI) that can be excited in the curved magnetic geometry characteristic of the terrestrial plasma sheet are investigated by means of three‐dimensional electromagnetic particle‐in‐cell simulations. Compared with earlier studies that considered a single Bz minimum configuration with an extremely large midtail field, additional simulations are performed in which this maximum is reduced to a more realistic value, the dependence on the values of the plasma beta and of the mass and temperature ratios mi/me and Ti/Te is investigated, and the limiting case of a constant Bz profile is examined. The general properties of the BICI modes are found to be unaltered by these changes. Significantly, the BICI excitation is found not to require an explicit tailward magnetic field gradient; it appears to be sufficient for the entropy to decrease with distance down the tail. The BICI wavelength varies inversely with Bz, and the eigenmodes are strongly field aligned with parallel electron flows comparable to the ion thermal velocity. In the edge of the plasma sheet, the oscillations in Bx and Bz have comparable magnitude. Once excited, the growth of the modes is robust and leads to the formation of intense interchange heads that propagate earthward. When the equatorial plasma beta is on the order of 500 or higher, the Bz field can be driven southward in the wake of the heads. This results in the onset of localized magnetic reconnection and a violent disruption of the plasma sheet.