[P-EM12] Coupling Processes in the Atmosphere-Ionosphere System

[PEM12-15] Investigation of Medium-Scale Traveling Ionospheric Disturbances using ISS-IMAP/VISI: Case Studies and Climatological Analysis

*Yuta Hozumi^1,2, Akinori Saito³, Michi Nishioka⁴, Takeshi Sakanoi⁵, Jia Yue^1,2, Min-Yang Chou^1,2, Satoshi Andoh⁴, Atsushi Yamazaki⁶, Yuichi Otsuka⁷, Kazuo Shiokawa⁷ (1.The Catholic University of America, 2.NASA Goddard Space Flight Center/CCMC, 3.Graduate School of Science, Kyoto University, 4.National Institute of Information and Communications Technology, 5.Planetary Plasma and Atmospheric Research Center, Tohoku University, 6.Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 7.Institute for Space-Earth Environmental Research, Nagoya University)

Keywords:Mid latitude ionosphere, Ionospheric disturbances, Airglow imaging

Nighttime medium-scale traveling ionospheric disturbances (MSTIDs) were investigated using 630 nm OI images from the Visible and Near-Infrared Spectral Imager (VISI) of the International Space Station - the Ionosphere, Mesosphere, Upper Atmosphere, and Plasmasphere Mapping (IIS-IMAP) mission. Although MSTIDs have been widely studied through ground-based observations, their global behavior remains less understood due to the geographical limitations of such measurements. Here, we present new insights into MSTID climatology derived from spaceborne observations. VISI’s dual fields of view, pointing forward and backward from the nadir, enable the discrimination of genuine ionospheric signals from ground-based light contamination. Case studies show that the forward and backward views capture subtle differences in MSTID structures, consistent with an equatorward-tilted vertical geometry of MSTIDs. Comparisons with simultaneous Total Electron Content (TEC) observations from the Japanese GNSS Earth Observation Network (GEONET) and ground-based all-sky imagers (OMTI) reveal that the measured wave parameters—wavelength, propagation direction, and amplitude—are in good agreement with established MSTID characteristics. An analysis of three years (2013–2015) of VISI data identified 676 MSTID events across both hemispheres, exhibiting strong seasonal and longitudinal variations. Local summer maxima and enhanced activity were observed in regions with high sporadic-E (Es) occurrence. In the Northern Hemisphere, the primary peak occurs around the June solstice, with particularly high rates in the Asia–West Pacific sector. In the Southern Hemisphere, a semiannual pattern emerges, featuring a primary peak during the December solstice and a secondary peak during the June solstice, also in the Asia–West Pacific sector. These findings suggest that Es-related E–F region coupling plays a key role in MSTID generation, with conjugate hemisphere coupling further modulating MSTID distribution.