[P-EM10] Dynamics of Magnetosphere and Ionosphere

[PEM10-P12] Multi-event study of 630-nm airglow enhancement during substorms based on ground-based observations in Japan

*Saki Morita¹, Kazuo Shiokawa¹, Yuichi Otsuka¹, Atsuki Shinbori¹, Sori Takuya¹, Akiko Fujimoto², Akimasa Yoshikawa³, Michi Nishioka⁴, Septi Perwitasari⁴ (1.Nagoya University Institute for Space-Earth Environmental Research, 2.Kyushu Institute of Technology, 3.Department of Earth and Planetary Sciences, Kyushu University , 4.National Institute of Information and Communications Technology)

The ionosphere is formed when part of the upper atmosphere above 80 km altitude is ionized by high-energy particles swept in from the solar ultraviolet and magnetosphere. The ionospheric plasma density distribution fluctuates due to both the electromagnetic energy input coming from solar planetary space and the energy input from atmospheric waves propagating upward from the lower atmosphere. Among them, it is known that during magnetic storms and substorms generated by solar wind energy flowing into the magnetosphere and polar ionosphere, two-cell polar-ionospheric convection is enhanced and expands equatorward. Ground-based observations have shown that a portion of that convective electric field penetrate into the mid-latitude ionosphere, causing the ionosphere to move up and down which in turn causes changes in the intensity of 630-nm airglow. In a previous study, Shiokawa et al. [2000] showed two events that airglow intensity fluctuates in time and space with storm time substorms using all-sky camera observations. The total electron content (TEC) of the ionosphere increased in response to the airglow enhancement, but ionosonde observations could not be observed change in the virtual height of the lower ionosphere with the electric field penetration associated with the substorm. In this study, we will observe changes in 630-nm airglow intensity associated with substorms at multiple stations and compare them with data of the Frequency Modulated Continuous Wave (FM-CW) radar operated by Kyushu University in order to clarify the causes of changes in airglow intensity. Our study used all-sky cameras installed at three stations in Japan (Rikubetsu (43.5^oN, 143.8^oE), Shigaraki (34.9^oN, 136.1^oE), and Sata (31.0^oN, 130.7^oE)) and FM-CW radar at Sasaguri (33.4^oN, 130.3^oE). We looked for events in which airglow intensity increased simultaneously at two or more stations during substorms and found five cases. The results show that such airglow enhancement is very rare. And these cases occurred regardless of the size of the magnetic storm or substorm. Airglow enhancement ranged from 100 to 400 R, with durations of 0.5 to 2 hours, and occurred below about 40^oN. During this airglow enhancement, the total ionospheric electron number above the stations of all-sky camera also increased by 0.1-0.4 TECU at the same time. And the virtual height of the ionosphere obtained by FM-CW radar for two of these cases was down during the event, but it was down before the onset of the substorm and did not change abruptly with the onset of the substorm. These are interesting results that characterize the electric field penetration into mid and low latitudes during substorms and the response of the ionosphere to it.