Oblique High Mach Number Heliospheric Shocks: the Role of Alpha Particles

Abstract:

Spacecraft observations of heliospheric shocks often show oscillations in the magnetic field and density, both upstream and downstream. The magnetic oscillations of oblique collisionless shocks were detected by Wind and DSCOVR with high temporal resolution of up to 50 samples/s. The density oscillations associated with the shocks are also evident in density by Wind (with lower temporal resolution). Recently, we have investigated low Mach number low-beta oblique shock oscillations using satellite data and 2.5D hybrid modeling with electrons modeled as fluid and ions modeled as particles and found that alpha particles may affect considerably the downstream oscillations and the shock structure. Here, we extend the study to high Mach number shocks (M>3), investigate several alpha particle typical densities, and compare the results. Using the 2.5D hybrid model we found that high Mach number quasi-perpendicular shock magnetic and density structures are significantly affected by alpha particles typical densities, manifesting in effect on rippling, nonstationarity, and reformation of the shocks. Multiple point spacecraft observations are needed to properly account for these shock features. We investigate the effects of alpha particles relative abundance on the shock ramp, wake, and downstream oscillation structure as well as kinetic properties of proton and alpha particle velocity distributions.