Japan Geoscience Union Meeting 2025

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[E] Oral

P (Space and Planetary Sciences ) » P-EM Solar-Terrestrial Sciences, Space Electromagnetism & Space Environment

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

Sun. May 25, 2025 10:45 AM - 12:15 PM 303 (International Conference Hall, Makuhari Messe)

convener:Keisuke Hosokawa(Department of Communication Engineering and Informatics, University of Electro-Communications), Huixin Liu(Earth and Planetary Science Division, Kyushu University SERC, Kyushu University), Yuichi Otsuka(Institute for Space-Earth Environmental Research, Nagoya University), Loren Chang(Department of Space Science and Engineering, National Central University), Chairperson:Takeshi Sakanoi(Planetary Plasma and Atmospheric Research Center, Graduate School of Science, Tohoku University), Elvira Astafyeva(Institut de physique du Globe de Paris)

11:45 AM - 12:00 PM

[PEM12-05] Evolution of Post-Sunset Equatorial Plasma Bubbles: Relationships to the Equatorial Ionospheric Anomaly Induced by Pre-Reversal Enhancement Electric Fields

*Lung-Chih Tsai1, Shin-Yi Su2, Jun-Xian Lv1 (1.Center for Space and Remote Sensing Research, National Central University, Taoyuan, Taiwan, 2.Department of Space Science and Engineering, National Central University, Taoyuan, Taiwan)

Keywords:post-sunset equatorial plasma bubble (EPB), equatorial ionospheric anomaly, equatorial spread F (ESF), GNSS radio occultation (RO) observation, scintillation

This paper presents GNSS radio occultation (RO) observational analyses on deducing the relationships and dependences between post-sunset equatorial plasma bubbles (EPB) occurrences and equatorial ionospheric anomaly (EIA) strength variability. The RO data were acquired from the FormoSat-7/Constellation Observing System for Meteorology, Ionosphere and Climate 2 (FS7/COSMIC2) Program from 2020 to 2024. In this study, we consider both impacts from crest electron density (Nemax) and crest-to-trough Nemax ratio and propose a new EIA strength (EAS) parameter defined as the summary of two crest-to-trough Nemax differences to recognize and characterize the post-sunset EIA features. Both seasonal–longitudinal appearances of intense post-sunset EPB occurrences and strong EIA events occurred on more or less 30 days expanded from when and where magnetic flux tubes align with the sunset terminator at the magnetic equator but have more intense EPB and/or strong EIA days during southern (northern) hemispheric summers in the South American area (the Central Pacific area and the Africa area). It is well consistent with Tsunoda’s hypothesis [1985] during the evening pre-reversal enhancement (PRE) and reveals more informationt on day-to-day variability, intensities and extents of post-sunset EPB occurrences and EIAs subject to seasonal, longitudinal, and solar cycle variability. Moreover, the local-time evolutions of peak post-sunset EIAs occurred during 19~20 LT which is earlier than that of the obtained experimental peak (i.e., 20:20 LT) of post-sunset EPB occurrences. We expect that the post-sunset EIA detection could be a potential precursor for post-sunset EPB occurrence.