On the origin of the quasi-perpendicular ion foreshock: Full-particle simulationsReport as inadecuate

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1 LPP - Laboratoire de Physique des Plasmas 2 HEPPI - LATMOS LATMOS - Laboratoire Atmosphères, Milieux, Observations Spatiales

Abstract : Many space missions have already evidenced the existence of the ion foreshock region located upstream of the Earth-s bow shock and populated by energetic backstreaming ions reflected by the shock front. In order to analyse this region, a curved shock is simulated with a 2-D particle-in-cell PIC code. The analysis is presently restricted to the quasi-perpendicular angular range defined by 45° ≤ θBn ≤ 90°. In agreement with experimental data, present results evidence two distinct ion populations back-streaming from the shock front along the interplanetary magnetic field: i the Field-Aligned Beam population hereafter -FAB- and ii the gyrophase bunched population hereafter -GPB- which differ from each other by their gyrotropic or non-gyrotropic behavior, respectively. Excluded by a simulation time which is too short, ion instabilities pitch-angle scattering cannot be the source of -GPB-. Two new criteria are proposed to identify more precisely each population: their interaction time Δtint with the shock front and their downstream penetration depth. These criteria show that i the -FAB- population moves back and forth between the upstream edge of the shock front and the overshoot, and is characterized by a Δtint covering several upstream gyro-periods. ii In contrast, the -GPB- ions suffer a short interaction time i.e. 1

Author: Philippe Savoini - Bertrand Lembège - Joël Stienlet -

Source: https://hal.archives-ouvertes.fr/


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