Structure of a Quasi-parallel Shock Front

Abstract

The aim of this study is to compare observations of the magnetic field structure of observed quasi-parallel collisionless shock fronts with the results obtained analytically. A two-fluid analytic model of the shock front structure was derived under the assumptions that the shock is stationary and planar. The ion and electron kinetic pressures were assumed to be scalar, and polytropic state equations were used. The results of this analytical approach show that the shock magnetic field has an oscillatory structure. Venus Express (VEX) observations of the Venusian bow shock have been used to validate these theoretical findings. The Venusian bow shock and corresponding foreshock are significantly smaller than those of Earth. Thus, observations of the underlying structure of the quasi-parallel shock at Venus are not masked by the presence of high-amplitude waves and nonlinear structures originating in the foreshock. It is shown that the structure of the shock front, as observed by VEX, has a very strong similarity to the structure obtained analytically.

Acceleration of Electrons and Ions by an “Almost” Astrophysical Shock in the Heliosphere

“…This finding is in line with theoretical predictions (Gedalin 1998;Gedalin et al 2015), which suggest that a quasi-parallel shock becomes oblique, even quasi-perpendicular, due to the increase in transversal magnetic field amplitude in the ramp-overshoot region. However, prior to our study, observational support for this was limited (Balikhin et al 2023). We have clearly demonstrated that the enhancement of the transversal magnetic field at the ramp overshoot leads to a quasi-perpendicular geometry.…”