Numerical modeling of electron energy-time dispersions in the high-latitude part of the cusp region

Abstract

We have constructed a one-dimensional numerical model of electron acceleration with dispersive Alfvén waves using realistic parameters based on a rocket observation in the high-latitude part of the cusp region. This paper demonstrates that our model could quantitatively reproduce important characteristics of observed electron energy-time dispersions, such as their fluxes, energy range, pitch angle distribution, and source altitudes. The energy-time dispersion at the rocket altitude is produced by a time-of-flight effect of magrietosheath-originated electrons accelerated by the resonant interaction with inertial Alfvén waves (lAWs) at altitudes of 2000 ̃ 6000 km. The higher-energy electrons are generated at higher altitudes. The energy-time dispersion changes according to three key parameters: wave power, perpendicular wavelength, and wave frequency. The wave power affects the flux and the maximum electron energy, and the perpendicular wavelength affects the source altitude calculated by the time-of-flight analysis, while the wave frequency (time period) affects the time width of the energy-time dispersion. We summarize a reasonable set of these parameters for a typical energy-time dispersion observed in the cusp/cleft region. Finally, we suggest that the lAWs are generated at the dayside magnetopause in association with magnetic reconnection and then propagate toward the ionosphere along the open field line connected to the magnetosheath. Their resonant acceleration of local electrons injected from the magnetosheath at altitudes of several thousand kilometers is the cause for multiple electron energy-time dispersions observed in the high-latitude part of the cusp region. Copyright 2005 by the American Geophysical Union.