[P-EM15] Space Plasma Physics: Theory and Simulation

[PEM15-P11] Numerical analysis of ionospheric polarization in the generation mechanism of poleward boundary intensification of auroral emission

*Masaru Morisawa¹, Akimasa Yoshikawa², Shinichi Ohtani³ (1.Kyushu University, 2.Department of Earth and Planetary Sciences, Kyushu University, 3.The Johns Hopkins University Applied Physics Laboratory)

Keywords:ionosphere, ionospheric polarization, PBI

We numerically investigated ionospheric polarization for revealing the generation mechanism of PBI, which stand for poleward boundary intensification, an auroral intensification at the poleward boundary of the auroral oval. Ohtani and Yoshikawa [2016] proposed the idea that PBI occurred associated with ionospheric polarization due to fast polar cap flows. While a general theory that PBI is the ionospheric manifestation of the distant reconnection in the magnetotail [e.g., Lyons et al., 2011] is difficult to explain the recently reported PBI characteristics [e.g., Zou et al., 2014], the new idea is consistent with them, so the new one is better than the old one. To prove this new theory, Ohtani and Yoshikawa [2016] conducted a numerical analysis and confirmed that Alfven waves reflect from the ionosphere due to ionospheric polarization. However, their analysis did not consider the effect of the evolution of ionospheric conductivity induced by precipitated electrons associated with field-aligned currents (FAC) and the advections in the perpendicular direction of magnetic lines, therefore only the initial process of PBI was investigated. In this study, our model includes the two effects and can investigate not only the initial process but also the time evolution of ionospheric polarization. As a result, it was found that the precipitated electrons are significant for the time variation of electric conductivity. Because of the effect, induced upward FAC changed in space, and we successfully reproduced the north-south structure of PBI. Also, in contrast to the small contribution of the Hall polarization in the initial process, upward FAC induced by Hall polarization is larger than the one by Pedersen polarization in the evolution process, suggesting the importance of the Hall polarization.