Relativistic electron precipitation as seen by NOAA POES

We performed a survey of relativistic electron precipitation (REP) events revealed by the Medium Energy Proton and Electron Detector instrument on board NOAA Polar-orbiting Operational Environmental Satellites during a 38day interval. We have divided the observed REP events into three groups with respect to the simultaneous observations of energetic (>30keV) electron and proton precipitation. The first group consists of REP enhancements forming the isotropy zone at the poleward edge of trapped relativistic electron fluxes. These REP events are observed on the nightside, and they are, apparently, produced by isotropization process related to nonadiabatic motion of particles in the stretched magnetic field. The second group are the REP events related to simultaneous enhancements of energetic >30-300keV electrons. These events have a wider magnetic local time range of occurrence with a maximum in the premidnight sector. They can be related to the interaction of electrons with waves whose possible nature is briefly discussed on the basis of comparison with the cold plasma density in the conjugated region of the equatorial plane. The third group consists of the REP events correlated with the burst-like precipitation of >30-keV protons within an anisotropy zone, where the trapped flux dominates. These events are found in the dusk sector in association with enhanced cold plasma density in the conjugate equatorial magnetosphere. As is known, proton bursts within the anisotropy zone indicate the location of the electromagnetic ion cyclotron (EMIC) wave source. Such REP events can be due to scattering of the relativistic electrons by EMIC waves. However, we noted that some of these REP events are associated with precipitation of energetic electrons with low-energy cutoff below 100keV. We suggest that in such cases the electrons within a wide energy range are precipitated by other waves (probably, by plasmaspheric hiss).