Oblique High Mach Number Heliospheric Shocks: The Role of α Particles

Abstract

AbstractSpacecraft observations of heliospheric shocks often find oscillations in the magnetic field and density both, upstream and downstream. The downstream magnetic oscillations of oblique collisionless shocks were detected by Wind with 10.9 samples s−1 and DSCOVR spacecraft with high temporal resolution of 50 samples s−1. The density oscillations associated with the shocks are also evident in proton and α particle density by Wind (with much lower temporal resolution). Recently, we have investigated low Mach number low‐β oblique shock oscillations using satellite data and 2.5D hybrid modeling with electrons modeled as fluid and ions modeled as particles and found that α particles—an important component of heliospheric plasma—may affect considerably the downstream oscillations and the shock structure. The objective of the present study is to investigate the effects of α particles on high Mach number heliospheric shocks dynamics, oscillations, nonstationarity, and shock‐front rippling. We extend the study to high Mach number shocks (M > 3), investigate several α particle typical densities, and compare the results for the various shock parameters. We model the effects of α particles on the shock ramp, wake, and downstream oscillation structure and the kinetic properties of proton and α particle velocity distributions at various locations downstream of the shocks. Using the 2.5D hybrid model we found that the modeled high Mach number quasi‐perpendicular shock magnetic and density structures are significantly affected by α particles with typical solar wind relative abundances, suggesting that the observed high Mach number shocks are similarly affected by α particles.