Collisional electrostatic ion cyclotron waves as a possible source of energetic heavy ions in the magnetosphere

Abstract

A new mechanism is proposed for the source of energetic heavy ions (NO+, O2+, and O+) found in the magnetosphere. Simulations using a multispecies particle simulation code for resistive current‐driven electrostatic ion cyclotron waves show transverse and parallel bulk heating of bottomside ionospheric NO+, O2+ and O+ ion populations. The dominant mechanism for the transverse bulk heating is resonant ion heating by wave‐particle ion trapping. Using a linear kinetic dispersion relation for a magnetized, collisional, homogenous, and multi‐ion plasma, it is found that collisional electrostatic ion cyclotron waves near the NO+, O2+, and O+ gyrofrequencies are unstable to field‐aligned currents of 50 µ A/m² for a typical bottomside ionosphere (<300 km altitude). A simple ion outflow model of heavy ions is formulated that verifies the assertion that a large number of energetic heavy ions originating from below 250 km can reach the topside ionosphere (>1000 km), and then via parallel electric fields be ejected into the Earth's magnetosphere.