Multiple energy‐dispersed ion signatures in the near‐Earth magnetotail: Geotail observation

Multiple energy‐dispersed ion signatures were observed by the Geotail spacecraft in the plasma sheet at ∼10 Re down the tail and ∼4 Re on the duskside, corresponding to a small and localized auroral intensification recorded by Polar/UVI. They were also accompanied by magnetic field dipolarization and enhancement of electron parallel pressure. All the dispersed signatures are interpreted as due to a time‐of‐flight effect of ion clusters produced in remote regions magnetically connected to the observation site. They can be categorized into two types in terms of energies and pitch angles. One is the higher‐energy components having crescent‐shaped distributions in the phase space and counterstreaming in the magnetic field direction. The other, of which the energy was dispersed from 2 keV down to 60 eV, was a collimated beam along the magnetic field line and unidirectionally streaming away from the Earth. The former is interpreted as bouncing ion clusters which are produced in a mid‐tail region with a similar process to the convection surge model, while the latter is most likely to be protons upflowing from the ionosphere. An interesting point in terms of the magnetosphere‐ionosphere coupling is nearly the simultaneous occurrence of ion accelerations in the mid‐tail region and above the ionosphere along the same field tube.