Two-dimensional simulations of a curved shock: Self-consistent formation of the electron foreshock

Philippe Savoini (1) , Bertrand Lembège (1)

1 CETP - Centre d'étude des environnements terrestre et planétaires

A collisionless curved shock is analyzed in a supercritical regime with the help of a two-dimensional electromagnetic full particle code. Curvature effects are included self-consistently and allow one to follow continuously the transition from a narrow and step-like strictly perpendicular shock to a wider and more turbulent oblique shock within the quasi-perpendicular range 65°<θBn<90°. Present results reproduce the formation of the electron foreshock without any simplifying assumptions. In agreement with experimental data, local bump-on-tail parallel distribution functions are well recovered in the foreshock region and correspond to electrons backstreaming along the magnetic field lines. Present detailed analysis shows that local back-streaming distributions have two components: (i) a high parallel energy component corresponding to back-streaming electrons characterized by a field-aligned bump-in-tail or beam signature, and (ii) a low-energy parallel component characterized by a loss cone signature (mirrored electron). Two types of bump-in-tail patterns, broad and narrow, are identified at short and large distances from the curved shock, respectively, and are due to different contributions of these two components according to the local impact of the time-of-flight effects. Present results allow one to identify more clearly the nature of the bump-in-tail pattern evidenced experimentally (narrow type). These also confirm that mirroring electrons make the dominant contribution to the bump-in-tail pattern in the total distribution in agreement with previous studies. Results suggest that low and high parallel energy populations are intimately related and may contribute together to the upstream wave turbulence.

Domaines: Géophysique [physics.geo-ph]; Physique de l'espace [physics.space-ph]

Philippe Savoini, Bertrand Lembège. Two-dimensional simulations of a curved shock: Self-consistent formation of the electron foreshock. Journal of Geophysical Research Space Physics, 2001, 106 (A7), pp.12975 - 12992. ⟨10.1029/2001JA900007⟩. ⟨hal-01646986⟩