High‐energy proton drift echoes: Multiple peak structure

Abstract

Many high‐energy proton drift echoes observed in association with magnetospheric substorms exhibit multiple fine‐structure peaks during the course of one or more of the echoes. Because of the difficulty in distinguishing between temporal, positional, pitch angle selection, and drift shell effects with instruments on a single satellite the identification of these as individual entities (as opposed to statistical variations in proton intensity or other effects) has not been convincingly established heretofore. We have examined energetic ion data from similar instruments on three widely spaced geosynchronous satellites, with the goal of establishing whether or not these multiple peaks are a persistent feature of the injection process. Our results suggest that multiple peaks are indeed a real feature of drift echoes. At least three quarters of the ion enhancements that result in drift echoes are made up of multiple‐peaked events. A very good correlation between the onset of the various peaks and detailed features observed in high‐latitude magnetograms is observed for some of the multiple peaked events. In fact, in their relation to the magnetograms, there seems to be a pairing of pulses; that is, with some dips in the magnetogram there appears to be two associated pulses. Various possible models for the production of multiple peaks, including the ion tearing mode instability in the plasma sheet, magnetic mirroring effects, temporal and/or positional effects of multiple neutral line formation, and effects due to different ion species are discussed.