Modeling the effects of α particles on collisionless oblique heliospheric shocks*

The α particles in the solar wind are the second most abundant ion, and can carry significant energy, momentum and mass flux. We investigate the effects of α particles on the dynamics and the oscillations in high-Mach number (M>3) oblique heliospheric shocks. However, detailed in-situ observations of α particle properties in these shocks are rare, in particular at high cadence on-par with the magnetic field measurements. The downstream magnetic oscillations in oblique collisionless heliospheric shocks were detected by Wind with 10.9 samples/s and recently by DSCOVR spacecraft with high temporal resolution of 50 samples/s. The ions were also detected by Wind, albeit  with lower temporal resolution then the magnetic oscillation. It is expected that Parker Solar Probe and Solar Orbiter will observe shocks in the inner heliosphere with detailed proton and α particle data with the expected increase of solar activity. Meanwhile, we report the results of 2.5D and 3D hybrid models of high Mach number shocks, where we investigate several α particle typical relative abundances, Mach numbers, and shock normal directions, and compare the results for the various shock parameters. In particular we model the effects of α particles on the shock ramp, wake, and downstream oscillations and study the kinetic properties of proton and α particle velocity distributions function (VDFs) downstream of the shocks. The modeling results demonstrate that with typical α particle solar wind abundances of 5% the dynamics and the oscillations of high-Mach number shocks is significantly affected, evident from comparison to proton only shock models. We discussed the implication of our modeling results to the interpretation of spacecraft observations.