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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.

The dependence of the charge exchange lifetimes on the mirror latitude for ions mirroring off the geomagnetic equator has been re‐computed using the improved hydrogen distribution models which have become available since the earlier calculation by Liemohn. The Chamberlain model, with the input parameters determined by recent satellite observations, has been used to define the spatial distribution of the neutral hydrogen environment through which the ring current ions traverse. The resultant dependence of the charge exchange lifetime, τ, on mirror latitude, λm, is best fit by the approximation τm = τe cos3.5λm, where τe is the charge exchange lifetime for the equatorial particles. This is a significant change from the cos6λm approximation of the previous results.

Intensity enhancements of the ring current electrons associated with the VLF emissions during the geomagnetic storms and substorms, which have been observed by the equatorially orbiting Sa-A satellite (Explorer 45), are so far limited only to electrons of energies below the order of 10 keV. Furthermore, onsets of the enhancement are detected in the lowest observable energy channel first, then shifting toward higher energies with time, a feature, which is opposite to the well-known energy dependence expected from the drift motion of electrons in the earth's dipole magnetic field. In order to explain these findings on the ring current electron enhancements, trajectories of electrons injected into the nightside of the magnetosphere from the geomagnetic tail are calculated by modifying Ejiri's calculations which were used for the interpretation of the nose events of the ring current protons observed also by the Sa-A satellite. The results indicate that the electron intensity enhancements are limited to electrons below the order of 10 keV simply because of the location of the observations which are initially confined to the dusk-midnight sector outside the plasmasphere. If the observations are made in the morning sector, where many VLF emissions such as chorus are observed, the enhancement should not be limited only to electrons below the order of 10 keV but should extend to electrons up to the order of 100 keV. The apparent inverse dispersion, i.e., the appearance of the enhancement at lower energies first, is also due to the location of the observations. Namely, if the observations are made in the morning sector outside the plasmasphere, the normal dispersion with the first enhancement by high-energy electrons should be seen. Since the adiabatic energy increase of charged particles during cross-magnetic field inward motion in the dipole field is largest for the 90 ø pitch angle particles, the energy at the source is lowest for 90 ø pitch angle electrons for the same energy at the observing location. The smaller enhancement of the small pitch angle electron intensity can therefore be explained by the energy spectra of source electrons in the geomagnetic tail.

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