ULF waves and their influence on bow shock and magnetosheath structures Original Research Article

We perform global hybrid (kinetic ions, fluid electrons) simulations of the solar wind interaction with a magnetized planet to study solar wind coupling for different dipolar field strengths and a variety of interplanetary magnetic field (IMF) geometries. The advantage of the hybrid code over fluid codes is that it treats ion-scale microphysics in the context of the global interaction. The shock and magnetosheath macrostructures are directly tied to ion kinetic processes and microinstabilities that generate ultralow frequency (ULF) waves in the foreshock and in the magnetosheath. We find that the quasi-perpendicular shock can form for obstacles with low magnetization and small size (relative to ion scales). In contrast, the quasi-parallel shock only forms when the scale size of the system is much larger than the ion inertial length, and depends on the generation of compressive waves. The foreshock is permeated by noncompressive waves generated by backstreaming beam ions, and by compressive fluctuations generated by beam-ring ion distributions. As compressive waves convect into the quasi-parallel region they evolve into large structures and form the shock transition. We find that variations of IMF geometry have a deep influence on magnetosheath structures and on the way that the plasma is heated and compressed.