Vorticity in the magnetospheric transition region of a global hybrid-Vlasov simulation

The transition region between the Earth's dipole field and the stretched magnetotail is a highly dynamic region of space where a variety of complex physical phenomena occur. The aim of this study is to understand the formation and evolution of large-scale plasma flow vortices in the transition region. The vorticity is found in the global magnetospheric hybrid-Vlasov model Vlasiator, which now features an ionospheric solver, enabling the study of magnetosphere-ionosphere coupling. We compare the results of the simulation to other magnetospheric simulations and observations of similar phenomena.

The vortices are highly structured and spread over the nightside with an azimuthal wavelength of about 3.5 RE (Earth radii). The vorticity in the magnetotail is induced by reconnection resulting in Earthward bulk flow with properties similar to bursty bulk flows (BBFs). In addition to BBF-like signatures, we observe that the features of the event are consistent with it originating from the ballooning/interchange instability, in combination with the fast Earthward flow. The fast flows and vorticity in the magnetosphere map onto the ionospheric grid of the simulation, and it can be seen that the Earthward flows create field-aligned currents. Our study investigates the formation of the vortices in the magnetotail, and the resulting ionospheric effects.