Role of helicon modes in the injection of oxygen ions in the ring current

Abstract

The presence of an ionospheric-origin anisotropic oxygen ion beam can excite a helicon mode instability in the near-Earth plasma sheet region. The helicon modes can be easily excited under the conditions when the usual long wavelength fire-hose modes are stable. The helicon modes are likely to attain saturation as the typical e-folding time of the instability is about a few minutes in the near-Earth plasma sheet region. Therefore, the instability could significantly affect substorm dynamics and lead to enhanced ionosphere–magnetosphere coupling. Low-frequency turbulence produced by these modes could scatter electrons trapped in the inner central plasma sheer region and help excite the ion tearing modes, leading to substorm onset. As a result, the oxygen ions would be injected into the Earth's nightside magnetosphere. Repeated injections by this process would lead to enhanced oxygen ion fluxes in the storm-time ring current.