The link between shocks, turbulence, and magnetic reconnection in collisionless plasmas

TLDR

Global hybrid and fully kinetic simulations of the magnetosphere have revealed a surprising interconnection between shocks, turbulence, and magnetic reconnection that appears generic in collisionless plasmas of space. Collisionless shocks with reflected ions can generate reconnecting current sheets and magnetic islands up to tens of ion inertial lengths. The study finds that reflected ions in collisionless shocks produce reconnecting current sheets, amplify low‑frequency waves that persist for many ion cyclotron periods before dissipating, and cause shock‑front rippling that launches high‑pressure jets which stir the downstream plasma, generating vortices, sunward flows, and flux ropes, thereby closing the loop between shocks, turbulence, and magnetic reconnection.

Abstract

Global hybrid (electron fluid, kinetic ions) and fully kinetic simulations of the magnetosphere have been used to show surprising interconnection between shocks, turbulence, and magnetic reconnection. In particular, collisionless shocks with their reflected ions that can get upstream before retransmission can generate previously unforeseen phenomena in the post shocked flows: (i) formation of reconnecting current sheets and magnetic islands with sizes up to tens of ion inertial length. (ii) Generation of large scale low frequency electromagnetic waves that are compressed and amplified as they cross the shock. These “wavefronts” maintain their integrity for tens of ion cyclotron times but eventually disrupt and dissipate their energy. (iii) Rippling of the shock front, which can in turn lead to formation of fast collimated jets extending to hundreds of ion inertial lengths downstream of the shock. The jets, which have high dynamical pressure, “stir” the downstream region, creating large scale disturbances such as vortices, sunward flows, and can trigger flux ropes along the magnetopause. This phenomenology closes the loop between shocks, turbulence, and magnetic reconnection in ways previously unrealized. These interconnections appear generic for the collisionless plasmas typical of space and are expected even at planar shocks, although they will also occur at curved shocks as occur at planets or around ejecta.