Sounding rocket observations of precipitating ions in the morning auroral region.

摘要

The origin of highly-structured ion fluxes measured by a sounding rocket launched into the morning auroral region on January 23, 1985 is investigated. The energy spectra of the precipitating ions exhibit an energy-time dependence in which particles of higher energies arrived at the rocket before those of lower energies. The spectra are interpreted as being due to the impulsive injection of particles onto high-altitude magnetic field lines, followed by their subsequent drift down the field lines to rocket altitudes. The dispersal to low energies with increasing time is explained as a time-of-flight effect in which the slower particles take longer times to traverse the distance. The ion signatures are used to constrain several possible physical models which characterize the source region. Source locations in the nightside magnetopause boundary layer are deduced through the examination of electron energy spectra and the use of a magnetospheric magnetic field model. The modeling efforts indicate that the data are consistent with sources located in the mid-latitude region of the flank boundary layer on the morning side of the magnetosphere, being in the range of 20-30 earth radii down the geomagnetic tail from the earth. Multiple injections of ions are observed, with a deduced quasi-periodicity of 100-200 s. Several candidate injection mechanisms are examined, with a mechanism related to the propagation of waves on the surface of the boundary layer found to be the most plausible explanation for the observations. Comparison is made to similar analyses by others and suggestions for future work are made.