On the Linearity of Mercury's Nightside Magnetosphere

Planetary magnetospheres are elaborate systems of internal and external factors, ranging from the internal planetary magnetic moment and currents in the magnetospheric boundaries to exosper-ionosphere-surface interaction, and variation in solar wind properties.In general, these flows and fields are usually interacting non-linearly.However, there are regions in the magnetosphere where properties may be understood in terms of a linear superposition.Here, we investigate the far downtail regions of the nightside magnetotail, where two key factors are the compressed but decreasing planetary magnetic field and the surrounding interplanetary magnetic field (IMF).Thus, we conduct 12 global model runs of Mercury's magnetosphere with 6 IMF directions in Cardinal and Parker Spiral directions each.We then superimpose 3 Cardinal IMF runs to emulate linear combined Parker Spiral (LC) IMF cases and compare these to the real Parker Spiral IMF case runs along the downtail passages of the MPO and Mio spacecraft of the BepiColombo mission.It is found that most LC cases share a surprising level of similarity with the real IMF cases for features such as the general tail twist, suggesting that some physical processes within the magnetotail may be described as linear, despite the overall interaction is non-linear.Finally, we further investigate approaches to the definition of a threshold of linearity.