Global dynamics of the Earth's plasmasphere

The structure and dynamics of the plasmasphere are highly sensitive to the geomagnetic disturbance activity that occurs regularly within the Earth's magnetosphere. The cycles of erosion and refilling of the plasma population in the plasmasphere have been studied extensively in the past but from the relatively limited perspective of individual (or occasionally multiple) ground stations and satellite crossings of the plasmapause and plasmasphere. Data available from the Extreme Ultraviolet Imager (EUV) on the IMAGE satellite allow us, for the first time, to study the plasmasphere system from a global perspective. The EUV instrument images the He+ distribution in the plasmasphere by detecting resonantly scattered solar 30.4-nm radiation and produces images encompassing the entire plasmasphere with approximately 640 km spatial resolution once every 10 minutes. By tracking the location of the plasmapause in sequences of EUV images, we make quantitative measurements of radial and azimuthal motions of the boundary during the various phases of geomagnetic disturbances. We examine the rapid inward motion of the plasmapause boundary on the nightside of the Earth, the formation and evolution of plasmaspheric "plumes", and the tendency for mesoscale azimuthal variations in the plasmapause radius to develop in a limited local time sector on the dayside. These disturbances represent periods of significant redistribution of mass within the magnetosphere, and using the global images, we estimate that 50 to 100 metric tons of material, constituting between 25% and 45% of the initial plasmaspheric distribution, is removed from a volume extending from 1.5 to 5.5 RE in a period of 15 hours or less. Finally, we identify an association between the plasmaspheric plume and energetic protons precipitating into the subauroral ionosphere. During a geomagnetic disturbance on June 18, 2001, a detached subauroral proton arc mapped along geomagnetic field lines to a broad region of enhanced cold plasma density associated with the plasmaspheric plume. The link between the proton arc and plasmaspheric plume suggests that the proton precipitation may be a result of wave-particle interactions which preferentially occur within the plume region.