Jovian magnetospheric responses to internal and external processes

Abstract

The complexity of the Jovian magnetosphere arises from Jupiter’s rapid rotation and the Io plasma source. Thus, physical processes of the Jovian magnetosphere are very different from that in the Earth’s magnetosphere and have yet to be fully understood. However, observations, theoretical models, and numerical simulations may not accurately reflect or explain some processes of the Jovian magnetosphere to a certain extent, and may even lead to some contradictions, for example: 1. According to the corotation breakdown model, the intensity of the Jovian auroral main emission is expected to decrease during solar wind compression (SWC) period. However, multiband observations have shown overall enhancement of the auroral emission during SWC, which contradicts the theoretical model. 2. Observations have shown that the location of Jovian magnetopause can vary rapidly and greatly. The drastic variation of the Jovian magnetopause location is generally believed to be caused by external conditions, i.e., drastic changes in the solar wind ram pressure. Moreover, most previous theoretical and numerical models are relatively symmetric and static for the internal Jovian magnetospheric conditions, such as the dynamics of the Jovian magnetodisc. Therefore, previous models lack detailed explanations for the effect of internal mechanisms on the drastic variations of the Jovian magnetopause. To investigate the important problems related to the physical processes of the Jovian magnetosphere being controlled by internal and external conditions, I conduct a series of three-dimensional global MHD simulations of the Jovian magnetosphere. Based on the results of the study, the thesis shows: 1. the simulations with SWC indicate that both upward field-aligned current and downward Alfvénic Poynting flux undergo nonlinear variations during SWC, which is consistent with change trend of the auroral UV power in observations. 2. the variation of Jovian magnetopause can be particularly dramatic, with the standoff distance near noon varying by up to 50 Jovian radii even under constant solar wind conditions. Moreover, the variation frequency of the magnetopause is very high, about once per 1 – 2 hours. 3. the mass loading rate of the Io plasma torus has a very important impact on the Jovian magnetodisc and even the entire Jovian magnetosphere. Specifically, the formation and transportation of the interchange structures and the evolution of the magnetodisc are greatly influenced by the mass loading rate. In summary, the study on the responses of the Jovian magnetosphere suggests that different Jovian auroral activities including brightening or dimming can be observed during SWC period, and the study provides new insights into future research themes on the interaction between the Jovian magnetosphere and the external environment. In addition, the study on the Jovian magnetosphere responses to internal conditions provides important new context for interpreting the Jovian magnetopause location and dynamics, with key implications for other internally mass-loaded and/or rapidly rotating systems.