The resolved layer of a collisionless, high β, supercritical, quasi‐perpendicular shock wave: 3. Vlasov electrodynamics
Authors: Scudder J. D. , Mangeney A. , Lacombe C. , Harvey C. C. , Wu C. S. , Anderson R. R. 
Published: February 2008

Strong evidence is provided that the self‐consistently determined deHoffman‐Teller electric field controls the lowest‐order deformation and structure of the observed parallel electron distribution throughout a well‐resolved, supercritical, quasi‐perpendicular shock wave. Details of this control include velocity space boundary features predicted by reversible Vlasov theory in the dc force fields. Phase space signatures of collisionless dissipation are also explicitly illustrated for the first time. The observed contrast between the reversible Vlasov prediction using the deHoffman‐Teller potential clearly demonstrates the onset of irreversibility and the causes for the loss of electron energy implied by the negative parallel resistivity determined in paper 2. These measurements quantitatively illustrate the primary role of the deHoffman‐Teller electric field in increasing the electron parallel “temperature” across the shock and the secondary role of wave‐particle reactions which actually “cool” the reversibly energized distribution. Electric and magnetic field wave measurements have been used to determine wavelengths and indices of refraction of the turbulence within the shock layer in order to identify the collective effects responsible for this “collisionless” dissipation. The kinetic, modified two‐stream instability is identified as the principal wave mode (based on energy content) in the magnetic pedestal; at the main magnetic ramp these modes are joined by lower hybrid drift (LHD) modes, and an electron acoustic mode appears to be excitable within the magnetic overshoot. The reduced electron distribution has been empirically shown for the first time to have two peaks in this regime, but not elsewhere in the shock layer. The electron acoustic mode appears to be the primary agent for the anomalous resistivity across the shock ramp and overshoot, having the appropriate effective collision frequency and morphology; the bulk of the wave power and probable thermalizing (agent for the ions is the MTSSW (modified two‐stream instability due to transmitted solar wind ions) and LHD modes. By simulation the MTSSW mode in high β regime stabilizes by forming flat‐topped electron distributions; it is suggested that the MTSSW mode can remove the edges of the reversible Vlasov distributions which already have the basic ingredients (such as full width at half maximum) of the observed sheath distributions, leaving the flat‐topped distribution that is observed. The lower hybrid drifts are localized and strongest in the magnetic ramp, and the wave turbulence decays with distance behind the downstream convected ion inertial length (CIIL2), consistent with the removal of the driving free energy for this mode, which is the cross‐field drifts of the distinguishable ion subpopulations along the shock normal with respect to the electrons. The Vlasov and observed behaviors are contrasted with the extant particle shock simulations, and their limitations discussed.