Investigating magnetospheric dynamics of quadrupole magnetic fields throughout the heliosphere.

Tuesday, 15 December 2020
Joe Caggiano, University of Oregon, Earth Sciences, Eugene, OR, United States and Carol S Paty, University of Oregon, Earth Sciences & Clark Honors College, Eugene, OR, United States
While purely quadrupolar intrinsic magnetic fields have not yet been observed in a planetary body, magnetospheres containing strong quadrupole magnetic moments are relatively ubiquitous in the solar system. Uranus, Neptune and Mercury each possess significant quadrupole magnetic moments in addition to their dipole moments. This combination can be represented as a magnetic dipole significantly offset from each planet's center. During a pole reversal, the dipole moment of Earth’s intrinsic magnetic field will weaken in favor of higher-order magnetic moments, particularly a quadrupole moment. Uranus and Neptune possess highly complex magnetospheric structures due to their intrinsic magnetic fields containing strong dipole, quadrupole and octopole moments, and due to their large obliquities and magnetic axes tilts. As a result, both ice giant magnetospheres experience large diurnal and seasonal variability as the orientation of their magnetic fields change with respect to the solar wind flow direction. In order to better understand how Dungey convection and corotation are affected by non-dipolar magnetic fields, we plan to isolate and investigate the magnetospheric plasma flows in quadrupole field configurations. We use a multi-fluid magnetohydrodynamic model along with derived analytical models of quadrupole convection dynamics to analyze the influence of magnetic quadrupoles on magnetospheric convection when interacting with the solar wind at 0.2 AU, 1 AU, 20 AU, and 30 AU. In certain geometric cases, quadrupole magnetic fields provide simplified topologies that interact with the solar wind to produce unconventional magnetospheric convection patterns which could contribute to destabilizing trapped plasma within the magnetospheric system. We also calculate the magnetospheric convection and corotational timescales for this spectrum of quadrupole planets to better constrain the influence of rotation rate and distance from the Sun.