Inference of the ring current ion composition by means of charge exchange decay

Abstract

The analysis of data from the Explorer 45 (S³‐A) electrostatic analyzer in the energy range 5–30 keV has provided some new results on the ring current ion composition. It has been well established that the storm time ring current has a decay time of several days, during which the particle fluxes decrease nearly monotonically. In the past, ring current studies have assumed or stated that hydrogen was the dominant ion in the earth's ring current. By analyzing the measured ion fluxes during the several day storm recovery period and assuming that beside hydrogen other ions were present and that the decays were exponential in nature, we were able to establish three separate lifetimes for the ions. These fitted decay lifetimes are in excellent agreement with the expected charge exchange decay lifetimes for H+, O+, and He+ in the energy and L value range of the data. This inference technique thus establishes the presence of measurable and appreciable quantities of oxygen and helium ions as well as protons in the storm time ring current; we also find indications that He++ may also be present under these same conditions. The existence of additional ions is not ruled out by this technique.