Global MHD Simulations of Uranus' Dynamic Interaction with the Solar Wind: Diurnal and Seasonal Variations

Uranus' strongly asymmetric internal magnetic field and the unusual, highly tilted orientation of its rotation axis with respect to the orbital normal combine to produce a highly dynamic magnetosphere that undergoes significant diurnal and seasonal variations. Data from the single flyby through Uranus' magnetosphere by the Voyager-2 spacecraft along with limited telescopic observations of its atmosphere and aurora only hint at how such magnetospheric reconfiguration takes place. Here we apply the BATSRUS magnetohydrodynamics (MHD) code to Uranus to simulate the global structure of its magnetosphere and examine how it varies through rotation cycles and between different seasons. Our global MHD simulation incorporates a realistic internal field model and adopts a high-resolution grid that allows us to resolve the fine structure of key magnetospheric boundaries. We have performed global simulations for near solstice and for equinox conditions that enable us to compare and contrast the behavior of Uranus' magnetosphere at different seasons. Comparison of our simulation results with the Voyager data indicates that our MHD model reproduces the global structure of Uranus' magnetosphere with high fidelity. We will show how Uranus' magnetosphere periodically changes its configuration as the internal dipole rotates. In particular, the model accounts for the unusual structure and temporal variation of the tail plasma sheet that was sampled by the Voyager spacecraft. We will also discuss the morphology and physical origin of the large-scale current systems extracted from our simulations, and their implications for understanding available auroral observations obtained by Voyager and the HST.