Microburst cusp ion precipitation observed with Reimei

Abstract

At an altitude of 610-670 km, the Japanese satellite Reimei was the first to discover a new type of ion injections into the topside ionosphere in or in the vicinity of the cusp. These ion injections, called Microburst Cusp Ion Precipitation (MCIP), were spatially embedded into the dominant precipitation of magnetosheath-like particles. They were observed in approximately one third of all cusp traversals, and were characterized by a relatively low energy (with less than a few hundred electron-volts) and relatively short-lived nature (with a typical lifetime of 1 to 2 s). The characteristic energy decreases with time (Type 1), and sometimes does not clearly exhibit energy-time dispersion (Type 3). Only one event exhibits the characteristic energy increasing with time (Type 2). Applying the time-of-flight model (in which higher energy ions arrive at the observation point first) and the velocity filter model (in which the characteristic energy decreases with distance from a source field line under the influence of perpendicular drift motion), we estimated the source distance from Reimei. This paper proposes that a localized electric field, probably associated with inertial Alfvén waves and/or ionospheric Alfvén resonator, could have been generated at short intervals in time or in isolated regions at an altitude less than 3000 km, which results in MCLPs accompanied with energy-time and energy-pitch angle dispersions observed at an altitude of 610 to 670 km. Copyright 2008 by the American Geophysical Union.