Particle acceleration in geospace and its association with solar events

Particle acceleration is a prominent feature of the geomagnetic storm, which is the prime dynamic process in Geospace the near-Earth space environment. Magnetic storms have their origin in solar events, which are transient disturbances of the solar atmosphere and radiation that propagate as variations of the solar wind elds and particles through interplanetary space to the Earth's orbit. During magnetic storms, ions of both solar wind origin and terrestrial origin are accelerated and form an energetic ring current in the inner magnetosphere. This current has global geomagnetic e ects, which have both physical and technical implications. Recently it has been shown that large magnetic storms, which exhibit an unusually energized ionospheric plasma component, are closely associated with coronal mass ejections (CMEs). This implies a cause/e ect chain connecting solar events through CMEs and the solar wind with the acceleration of terrestrial ion populations which eventually constitute the main source of global geomagnetic disturbances. Here we present spacecraft observations related to storm-time particle acceleration and assess the observations in the framework of causes and e ects of solar-terrestrial relationships.