Quasi-electrostatic instabilities in storm time ring current

Ionospheric-origin oxygen ions form a substantial component of the ring current during magnetic storms and the most prominent component during intense storm. The storm time ring current is populated with energetic ions which provide a free energy for plasma instabilities. A dispersion relation for quasi-electrostatic low-frequency modes is derived by considering three-component plasma consisting of isotropic electrons and both proton and oxygen ions having Dory-Guest-Harris (DGH) type loss cone distributions. The dispersion relation is studied numerically for the ring current parameters. Saturation level of the excited modes is calculated by invoking the trapping of ions by the waves. Both proton and oxygen ions could be scattered into the loss-cone by interacting with these waves, leading to the ring current decay.