Non-substorm transient injection events in the ionosphere and magnetosphere

Abstract

High resolution ground-based observations in combination with observations made in the central plasma sheet by the ISEE-1 and -2 spacecrafts provided evidence for a new morphological class of transient events—plasma injections. They occurred in the nightside magnetotail during periods of prolonged steady convection without any activity of the type traditionally attributed to substorms. The main ionospheric signature of the plasma injections was an enhancement of equatorward plasma flow for a few minutes. The flow came into the STARE field of view at Λ ⩾ 70° and then proceeded equatorwards with a speed of 800–1000 km s −1. Its leading edge was often rather sharp (⩽20 km). In the central plasma sheet region, at r ∼ 20 R e, the main signatures were transient enhancements in the earthward convection speed and a rise of the B 2 component as well as the total magnetic field. They were sometimes accompanied by energetic particle bursts. Using the high time resolution measurements of the ISEE satellite pair it was possible to determine more about the structure of the fast spikes. The leading edge of the propagating disturbance was often quite sharp but could not be classified as any simple type of planar discontinuity. The observed features are discussed in terms of transient plasma injections produced by impulsive enhance- ments in the reconnection rate in the distant tail