[P-EM09] Dynamics of Magnetosphere and Ionosphere

[PEM09-16] A generation process of “Great Wall” aurora seen from ISS

*Sota Nanjo¹, Morio Tanaka², Natsuo Sato³, Yuta Hozumi¹, Keisuke Hosokawa¹, Ryuho Kataoka^3,4, Yoshizumi Miyoshi⁵, Shin-ichiro Oyama^3,5,6, Mitsunori Ozaki⁷, Kazuo Shiokawa⁵, Satoshi Kurita² (1.The University of Electro-Communications, 2.Kyoto University, 3.National Institute of Polar Research, 4.SOKENDAI, the Graduate University for Advanced Studies, 5.ISEE, Nagoya University, 6.University of Oulu, 7.Kanazawa University)

Keywords:Omega band, Field-Aligned Current, Magnetosphere-Ionosphere coupling

By analyzing observations of the digital single-lens reflex cameras onboard the International Space Station, we have reported the morphology of the "Great Wall" aurora, which is a structure, embedded within the omega-band aurora, having wide distributions in the latitudinal and altitudinal directions and a narrow extent in the longitudinal direction. By studying the two case examples from both hemispheres, we found that the Great Wall auroras appeared in the western flank of the torch structure of the omega-band. We also showed the detailed structure of the Great Wall aurora at the JpGU-AGU meeting last year. However, we have not yet discussed their generation process in detail. To better understand the generation process of the Great Wall aurora, it is important to discuss the current system in the vicinity of the omega-band. Vanhamäki et al. (2009) derived the current system in the vicinity of the omega-band by combining model calculations with observations using optical instruments, a riometer, and magnetometers. Their results suggest that there is an upward field-aligned current (FAC) in the western flank of the torch structure due to the negative divergence of the electric field. The existence of the upward FAC is consistent with the appearance of the Great Wall aurora, but they did not discuss how the optical aurora forms in that region as a manifestation of FAC. In this study, we focus on the gradient of the conductance of the torch structure and discuss the possible generation process of the Great Wall aurora. Within the hole structure, a dark region between the consecutive torches, conductance is lower as compared to that in the torch structure; thus, the positive (negative) charges are accumulated along the western (eastern) flank to keep the westward flowing Hall current continuous. The positive potential along the western flank can increase the electron precipitation and drives the upward FAC, which can introduce the generation of Great Wall aurora. In the presentation, we will discuss the validity of this scenario by analyzing observations from the low-Earth orbiting satellites.