Plasma processes at collisionless shock waves

The importance of the curvature of the Earth bow shock surface for particle acceleration is discussed. Plasma quantities at collisionless shock waves obey the generalized Rankine-Hugoniot relations. Four parameters are considered: the magnetosonic Mach number, the angle between the shock normal and the upstream magnetic field direction, the ratio of particle pressure to magnetic pressure, and the electron to ion temperature ratio. At low Mach number (M or = 3), the shock is resistive. Between M = 3 and M = 5, viscosity is needed to dissipate the solar wind energy. Above M = 5, ion gyration becomes important with the dissipation length on the order of one or several ion gyroradii. Both electromagnetic and electrostatic turbulence were observed. Two processes for accelerating particles seem to be working at the Earth bow shock: one based essentially on the electric field tangent to the shock seen by particles trying to move upstream; the other working on particles already accelerated with the previous mechanism, being a Fermi-like mechanism and operating in front of quasi-parallel shocks.