Electron Vortex Generation in Earth's Collisionless Bow Shock: MMS Observations

In astrophysics and space, supercritical shock is generated when an object interacts with an incoming supersonic plasma stream. Its downstream plasmas are highly turbulent, containing abundant vortices on all scales from magnetohydrodynamic to electron gyroscales. Understanding the production of these vortices is at the forefront, especially on the electron scale. Using ultrafast measurements of NASA's Magnetospheric Multiscale spacecraft, we report on the fortunate multi-spacecraft observation of the formation of an electron vortex directly generated inside the Earth's quasi-parallel bow shock transition and propagated to the downstream turbulent magnetosheath. The vortex is generated inside the shock transition by anisotropic ∼100–600 eV electrons trapped in an ion-scale magnetic hole which could show a tornado-like magnetic morphology. Our results demonstrate that the electron vortex can develop not only as a product of the forward cascade but also from the shock transition into its downstream turbulence, which adds to the short-scale turbulence and dissipation.