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

Abstract. 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.