Paper#: 26
Poster #:
Session Name: Workshop 4A: Tail Instabilities
Room: 200ABC
Day: Tuesday
Time: 1:30-1:55 p.m.
Abstract Title: Acceleration and Convection of Particles in the Mid-tail during Substorms
PresentSurname: Delcourt, D.C.
All Authors: D.C. Delcourt
Abstract : During the expansion phase of substorms, short-lived reconfigurations of the magnetic field lines due to changes in the magnetospheric current system are responsible for prominent induced electric fields that lead to localized convection surges. Using single-particle simulations and data from various spacecrafts, we review some features of charged particle dynamics during such reconfigurations of the inner (~10 RE) magnetosphere. In particular we show that, in the parallel direction, ions traveling at low latitudes are subjected to prominent equatorward oriented acceleration due to the rapid direction-changing ExB. This centrifugal effect leads to focusing of ions with relatively small parallel speeds in the equatorial region, which in turn yields the development of substantial (several kVs) parallel potential drops and the production of magnetic field-aligned electron beams. On the other hand, in the perpendicular direction, particles may experience abrupt nonadiabatic heating when their gyroperiod is comparable to the field variation time scale. As an example, O+ ions expelled from the ionosphere may be accelerated up to hundreds of keV while being injected earthward, hence providing a seed population for the outer ring current. This process may be at the origin of the enhanced O+ contribution observed during storm times. More generally, these results suggest that electric fields induced by relaxation of the magnetic field lines play an active role in the dynamics of the inner magnetosphere during the main phase of geomagnetic storms.