Crescent-shaped electron velocity distribution functions formed at the edges of plasma jets interacting with a tangential discontinuity

In this paper we discuss numerical simulations that illustrate a physical mechanism leading to the formation of crescent-shaped electron velocity distribution functions at the edges of a high-speed plasma jet impacting on a thin, steep and impenetrable tangential discontinuity with no magnetic shear. We use three-dimensional particle-in-cell simulations to compute the velocity distribution function of electrons in different areas of the plasma jet and at different phases of the interaction with the discontinuity. The simulation set-up corresponds to an idealized, yet relevant, magnetic configuration likely to be observed at the frontside magnetopause under the northward interplanetary magnetic field. The combined effect of the gradient-B drift and the remote sensing of large Larmor radius electrons leads to the formation of crescent-shaped electron velocity distribution functions. We provide examples of such distributions measured by a virtual satellite launched into the simulation domain.</p

Kinetic simulations of solar wind plasma irregularities crossing the Hermean magnetopause

Context. The physical mechanisms that favor the access of solar wind plasma into the magnetosphere have not been entirely elucidated to date. Studying the transport of finite-sized magnetosheath plasma irregularities across the magnetopause is fundamentally important for characterizing the Hermean environment (of Mercury) as well as for other planetary magnetic and plasma environments. Aims. We investigate the kinetic effects and their role on the penetration and transport of localized solar wind or magnetosheath plasma irregularities within the Hermean magnetosphere under the northward orientation of the interplanetary magnetic field. Methods. We used three-dimensional (3D) particle-in-cell (PIC) simulations adapted to the interaction between plasma elements (irregularities or jets) of a finite spatial extent and the typical magnetic field of Mercury’s magnetosphere. Results. Our simulations reveal the transport of solar wind plasma across the Hermean magnetopause and entry inside the magnetosphere. The 3D plasma elements are braked and deflected in the equatorial plane. The entry process is controlled by the magnetic field gradient at the magnetopause. For reduced jumps of the magnetic field (i.e., for larger values of the interplanetary magnetic field), the magnetospheric penetration is enhanced. The equatorial dynamics of the plasma element is characterized by a dawn-dusk asymmetry generated by first-order guiding center drift effects. More plasma penetrates into the dusk flank and advances deeper inside the magnetosphere than in the dawn flank. Conclusions. The simulated solar wind or magnetosheath plasma jets can cross the Hermean magnetopause and enter into the magnetosphere, as described by the impulsive penetration mechanism