Relativistic electron dynamics in the inner magnetosphere - a review

The dynamics of relativistic electrons in the inner magnetosphere around the time of geomagnetic disturbances have received considerable attention in recent years. In addition to the environmental impact these electrons have on space-hardware in MEO and GEO orbits, and their obvious impact on space weather, the scientific issues surrounding the transport, acceleration and loss of these particles in the inner magnetosphere have not been fully resolved. One of the prime difficulties in understanding the dynamics of relativistic electrons is their somewhat uncorrelated behavior with regard to the major solar wind drivers of the Earth's magnetospheric dynamics (solar wind velocity, density and magnetic field strength/direction) and the major indices representing these dynamics (Dst, Ae, Kp). Relativistic electrons observed at geosynchronous altitude reach their peak several days after the onset of a magnetic storm, and a wide range of responses can occur for seemingly similar geomagnetic disturbances/storms. We give here a review and comparison of the current state of research into relativistic electron dynamics, covering simple diffusion, substorm acceleration, ULF wave acceleration, recirculation by ULF waves or plasmaspheric hiss. We present the results of a recent statistical study which has identified the presence of sufficient ULF wave power for a duration of at least 12 h during a storm as being the most geoeffective indicator of subsequent relativistic electron enhancements at geosynchronous altitudes. For completeness we also briefly examine some of the problems and ideas related to relativistic electron losses. Published by Elsevier Science Ltd.