Wedge-like dispersion of sub-keV ions in the dayside magnetosphere: Particle simulation and Viking observation

Abstract

Particle drift simulation of low-energy ions (less than a few keV) with a simple geomagnetic field (dipole) and the Volland-Stern type convection electric field is found to be capable of investigating dispersed sub-keV ion events deep inside the dayside ring current region observed by Viking. Here we show three types of such events and simulation results. From the shape of the dispersion in the energy-latitude diagrams, they are called wedge-like dispersions: type 1 (characteristic energy monotonically increasing with latitude), type 2 (energy increasing with latitude, and subsequently decreasing with latitude), and type 3 (energy monotonically decreasing with latitude). All these cases are understood as results of energy-dependent drift motion of ions coming from the nightside near-Earth tail if the distribution function in the source region varies in time and space. The results indicate that the wedge-like ion dispersions even may be associated with a substorm injection and/or a localized plasma flow channel in the near-Earth tail. Copyright 2001 by the American Geophysical Union.