Multifluid Simulations of Kinetic Alfven Wave Resonances in Jovian and Terrestrial Magnetospheres

Field line resonances (FLRs) form as eigenmodes of Alfven waves between conductive ionospheric boundaries along magnetic field lines. Transverse density and Alfven speed gradients induce phase mixing in FLRs, developing kinetic wave signatures when perpendicular wavelengths are comparable to the ion acoustic gyroradius or the electron inertial length. When kinetic Alfven waves develop along an FLR, electron inertial effects can lead to dispersive wave trains that in turn can accelerate particles along the field line.

The Jovian magnetosphere has an inverted radial Alfven speed profile compared to the Terrestrial magnetosphere, due to density gradients at the Io plasma torus. This difference, combined with the deviations from a simple dipolar magnetic field profile, creates a host of environments for FLRs to form and phase mix. A variety of drivers populate FLRs in these contrasted environments, such as mode-conversion from pressure-driven waves (from the solar wind or Kelvin-Helmholtz instabilities), bursty bulk flows due to reconnection, and moon-plasma interactions, like the Alfven wings at Io.

To address these nonlinear processes, we present a 3D time-domain multifluid plasma simulation of FLRs which captures this nonlinear transition. An adaptive dipolar coordinate grid supports the deviations to the background field at Earth and Jupiter naturally, and an electron fluid is assumed to follow the heavier ion populations in a proton fluid and a heavier ion proxy fluid (oxygen at Earth, and a combination of oxygen and sulfur at Jupiter). Finitely conducting ionospheric boundaries couple poloidal and toroidal resonant modes in a current sheet with Pedersen and Hall conductivities. A finite volume 2nd order sub-grid spatial integrator scheme estimates the fluids and fields over a Runge-Kutta 4th order time step. This model approach provides the framework for deeper investigations of kinetic plasma ULF wave dynamics at Jupiter and Earth.