A multi-fluid MHD investigation of the magnetic quadrupole influence on the inner magnetosphere of Uranus

Uranus, the largest ice giant in the Solar System, is well known for its unconventional magnetic field. For simplicity, this magnetic field is often represented in magnetosphere models as an offset, tilted magnetic dipole. However, this appearance of an offset, tilted dipole is the result of the contribution of higher-order magnetic moments to the Uranian magnetic field. While the dipole moment is the strongest magnetic field contribution at the magnetopause boundary, the higher order moments, such as the quadrupole moment, become more pronounced in the inner magnetosphere.To study the influence of the quadrupole moment on the inner magnetosphere of Uranus, we performed multi-fluid MHD simulations implementing the spherical harmonic model of Uranus' internal magnetic field at solstice derived from the Voyager 2 flyby (Connerney, et al. 1987), and we rotate this magnetic field data to simulate Uranus at both solstice and equinox. We then compare the results to the offset tilted dipole field model. Specifically, we compare the structure and stability of corotational plasma and magnetospheric convection to highlight and quantify differences between these magnetic field representations. These differences may prove important for understanding Uranus' inner magnetospheric dynamics in general, as well as quantifying upstream conditions at Uranus' inner icy moons in support of the upcoming Uranus Orbiter and Probe mission.