Magnetospheric Responses to Solar Wind Pc5 Density Fluctuations: Results from 2D Hybrid Vlasov Simulation

Ultra-low frequency (ULF) waves in the Pc5 range, with periods between 150 – 600 s, play a key role in the dynamics of Earth’s magnetosphere, in particular through their interaction with radiation belt electrons. One important source of magnetospheric Pc5 waves are fluctuations of the upstream solar wind parameters in the same frequency range. Pressure variations in the solar wind are thought to result in a forced breathing of the magnetosphere, as the magnetosphere would expand and compress in response to the changing upstream conditions, which drives ULF waves inside the magnetosphere. The details of the interaction of these solar wind variations with the Earth’s bow shock and magnetosheath, their impact on the magnetosheath plasma properties and how the fluctuations would change before reaching the magnetopause, remain however unclear. In this study, we investigate the influence of externally-driven variations across near-Earth space using global 2D simulations performed with the hybrid-Vlasov model Vlasiator. The new time-varying boundary setup in Vlasiator allows us to set Pc5 periodic density pulses coming from the upstream. The density pulses cause the breathing motion of the bow shock, create clear stripes of variations inside the magnetosheath, and modulate the electromagnetic ion cyclotron (EMIC) and mirror modes. We characterize the spatial-temporal variations of waves on the simulation plane within the magnetosheath and discuss the potential impact on the near-Earth environment.