Magnetospheric convection in a hybrid-Vlasov simulation

Abstract. The Dungey cycle is a fundamental process governing large-scale plasma dynamics in the near-Earth space, traditionally examined through Magnetohydrodynamic (MHD) simulations and ionospheric observations. However, MHD models often oversimplify the complexities of driving dynamics and kinetic processes, while observational data tend to lack sufficient coverage. In this study, we utilize a hybrid-Vlasov simulation to investigate the Dungey cycle, and introduce a novel method for quantifying reconnection voltages in different Magnetic Local Time (MLT) sectors. This method is validated by comparing it with the ionospheric open flux change rate in the simulation. Our analysis identifies discrete azimuthal convection channels of closed field lines, clearly initiated by dayside reconnection and propagating to the nightside. These channels are prominent even during intervals of intense nightside reconnection. Notably, we observe that the effective length of dayside reconnection fluctuates, even under steady solar wind conditions. Our results reveal significant deviations from MHD theory, which predicts that plasma flows within the magnetosphere should follow flux tube entropy isocontours. Instead, we demonstrate that plasma flows near reconnection sites and at the terminators deviate from isentropic behavior, suggesting the presence of non-adiabatic processes in these regions. This study validates the representation of the Dungey cycle in the Vlasiator 3D simulation and enhances our understanding of global plasma convection. Future work should focus on identifying the kinetic processes that explain the deviations in the plasma convection with flux tube entropy isocontours between MHD theory and kinetic approach.