A Simulation Study of the Relationship Between Tail Dynamics and the Aurora

Abstract

AbstractThe Earth’s magnetotail goes through large scale changes during geomagnetically disturbed times that result in the earthward propagation of dipolarization events in the magnetotail containing highly energetic particles and a heightened electron precipitation into the ionosphere. During the 11 March 2008 substorm, earthward-propagating dipolarization fronts were observed by THEMIS spacecraft in the near-Earth magnetotail plasma sheet, and auroral brightening was observed by all-sky cameras at high northern latitudes around 70° in the pre-midnight sector. Using large-scale kinetic simulations along with spacecraft and ground-based observations, the properties (location, flux, energy, etc.) of precipitating particles were determined. We find that ~keV electrons in the region modeled by the simulation precipitate into the pre-midnight sector between about 68° and 72° due to two different physical mechanisms. Precipitation at higher latitudes is due to non-adiabatic pitch angle scattering that occurs at about 20–25 RE down tail, eastward of the reconnection region. The lower latitude precipitation is due to Fermi acceleration, which causes adiabatic electrons to enter the loss cone closer to the Earth, 10–15 RE downtail of the dipolarization front. The location, timing, and energy of electrons precipitating via these two mechanisms are in good agreement with all-sky camera images of auroral brightening observed at substorm onset.KeywordsSolar WindCurrent SheetPitch AnglePlasma SheetLoss ConeThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.