Global hybrid-particle simulations of Mercury's ion foreshock and ULF waves

We present analyses of ultra-low frequency (ULF) waves in Mercury's ion foreshock in our global hybrid particle-in-cell simulation code, RHybrid (paRallel Hybrid). The model treats ions as macroscopic particle clouds moving under the Lorentz force while electrons are a charge-neutralising, massless fluid. Magnetic field is advanced by Faraday's law and coupled self-consistently with ion dynamics (ion charge density and ion electric current density) via non-radiative Maxwell's equations. Mercury is described as a particle absorbing obstacle with a dipole magnetic field.

We study a broad parameter space of scenarios for the interplanetary magnetic field (IMF) and solar wind at Mercury, in particular analysing the properties of the resulting ion foreshock and associated ULF waves, such as the power spectral density, frequency, wavelength, phase speed, and polarisation among others, as well as the velocity distribution of the scattered suprathermal ions. We also compare these results among the different scenarios to investigate the response of the ion foreshock to different IMF (field strength, Parker spiral angle) and solar wind conditions (slow, moderate and fast stream).

With this work, we prepare for further development of the Finnish Meteorological Institute's free and open source space weather particle simulation platforms, and for the interpretation of upcoming observations from the BepiColombo mission.