Ac Electric and Magnetic Fields and Collisionless Shock Structures

Abstract

Instruments on board Pioneer 8 and 9, and OGO 5 have provided high time resolution plasma diagnostics from which the gross and fine structure of collision-free shocks can be deduced. We have found several types of shock structures in the high beta (β≈1) high Mach number (MA ≈ 10) flows of solar wind plasma impinging upon the magnetospheric obstacle and in the low Mach number interplanetary shocks. By far the most common structure is a large amplitude MHD pulse structure having a characteristic length of the initial gradient and trailing wavetrain corresponding to a few times c/ωpe, the electron inertial length. The dissipation mechanism in such shock structures is provided by electrostatic wave turbulence arising apparently from current driven electron-proton or proton-proton two stream instabilities which saturate nonlinearly. Nonlinear whistler mode waves also occur in some shock structures, but provide much less efficient dissipation or proton thermaliza-tion compared with that due to the electrostatic turbulence.KeywordsSolar WindMach NumberShock StructureHigh Mach NumberAlfven WaveThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.