Collisionless electrons in a thin high Mach number shock: dependence on angle and b

M. Gedalin (1) , E. Griv (1)

1 Department of Physics [Beer-Sheva]

It is widely believed that electron dynamics in the shock front is essentially collisionless and determined by the quasistationary magnetic and electric fields in the shock. In thick shocks the electron motion is adiabatic: the magnetic moment is conserved throughout the shock and v²_^ ? B. In very thin shocks with large cross-shock potential (the last feature is typical for shocks with strong electron heating), electrons may become demagnetized (the magnetic moment is no longer conserved) and their motion may become nonadiabatic. We consider the case of substantial demagnetization in the shock profile with the small-scale internal structure. The dependence of electron dynamics and downstream distributions on the angle between the shock normal and upstream magnetic field and on the upstream electron temperature is analyzed. We show that demagnetization becomes significantly stronger with the increase of obliquity (decrease of the angle) which is related to the more substantial influence of the inhomogeneous parallel electric field. We also show that the demagnetization is stronger for lower upstream electron temperatures and becomes less noticeable for higher temperatures, in agreement with observations. We also show that demagnetization results, in general, in non-gyrotropic down-stream distributions.

Domaines: Océan, Atmosphère; Sciences de la Terre

M. Gedalin, E. Griv. Collisionless electrons in a thin high Mach number shock: dependence on angle and b. Annales Geophysicae, 1999, 17 (10), pp.1251-1259. ⟨hal-00316675⟩