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

The presence of an ionospheric-origin anisotropic oxygen ion beam can excit e a helicon mode instability in the near-Earth plasma sheet region. The hel icon modes can be easily excited under the conditions when the usual long w avelength fire-hose modes are stable. The helicon modes are likely to attai n saturation as the typical e-folding time of the instability is about a fe w minutes in the near-Earth plasma sheet region. Therefore, the instability could significantly affect substorm dynamics and lead to enhanced ionosphe re-magnetosphere coupling. Low-frequency turbulence produced by these modes could scatter electrons trapped in the inner central plasma sheer region a nd help excite the ion tearing modes, leading to substorm onset. As a resul t, the oxygen ions would be injected into the Earth's nightside magnetosphe re. Repeated injections by this process would lead to enhanced oxygen ion f luxes in the storm-time ring current. (C) 2001 Elsevier Science Ltd. All ri ghts reserved.