Theoretical and hybrid modeling studies of quasi-perpendicular shocks in the heliosphere

Collisionless shocks result from Coronal Mass Ejections propagating in the heliosphere, and in regions of interaction between the solar wind and solar system bodies. The magnetized shocks efficiently convert the energy of the directed ion flow into gyration energy of particles behind the shock front. Downstream ions play the key role in the postshock dynamics, including development of instabilities and eventual thermalization of the plasma. We use theory and 2D hybrid modeling to study the formation of the downstream ion distributions, on the basis of ion dynamics in a stationary shock fronts. The study is motivated by STEREO observations of interplanetary shocks, as well as by Cluster, and THEMIS measurements at the Earth bow shock. We study low-Mach number shocks dominated by 1D evolution, as well as high-Mach number shocks where shock-front distortion and rippling takes place. The rippling affects ion acceleration and heating. Higher-Mach number shocks are no longer planar at the scales of the ion convective gyroradius and the local shock normal may differ substantially from the global normal. The 2D hybrid modeling approach allows full kinetic nonlinear description of the proton and ion motions, wave-particle interactions for parallel propagating and oblique waves, and velocity distributions in the magnetized plasma of the shocks, thus advancing our understanding of the rippling mechanism and the effects on the ions. We find that the angle between the local normal and the global normal may be as large as 40 degrees within the front of a rippled heliospheric shock.