On the Relation Between FORMOSAT-7/COSMIC-2 Radio Occultation Scintillation S4 Index and Co-located Electron Density Profiles in 2020
Y Duann, L. Chang, C. Chao, C.-Y. Lin, J.-Y. Liu, Dept. of Space Science and Engineering & Center for Astronautical Physics and Engineering, National Central University, Taoyuan City / National Tsing Hua University, Taiwan; T.-Y. Hsiao, Nuclear Science and Technology Development Center, National Tsing Hua University, Taiwan; S.-P. Chen, Dept. of Earth Sciences, National Cheng Kung University
Six Low earth orbiting FORMOSAT-7/COSMIC-2 (F7/C2) satellites were launched into 24° inclination on June 25th, 2019. The F7/C2 onboard payload: the primary Tri-GNSS (Global Positioning System—GPS, GALILEO, and GLObal NAvigation Satellite System—GLONASS) RO System (TGRS) offers a great opportunity of resolving ionospheric profiles during the 2020 solar minimum. The result of F7/C2 data sampling density with unfilled bins on a 30°-longitude and 1-hr local time (LT) grid of each month reveals that the unfilled percentage of the ionospheric scintillation profile with a maximum (S4 max) > 0.125 in 2020 is lower than 30% within geomagnetic latitude ±15°N. This indicates a level of sampling sufficient to resolve the planetary scale distribution of S4 at sub-harmonic time scales within the equatorial and tropical regions. A connection between S4 max > 0.125 and LT frame wave-2 tidal forcing is observed as in the numerical experiments by Chang et al. (2021). The altitudes of S4 max, the co-located (within a 30-minute time difference of and ~1° of longitude and latitude spatial difference) height of peak electron density in the F2-layer (hmF2), and the co-located maximum gradient of electron density at the bottomside F-layer are compared within 18 – 06 LT in this study, to study the occurrences and growth rate of equatorial plasma bubbles (EPBs) caused by plasma uplift after sunset. The winter anomaly (WA) of the strong S4 max (> 0.5) occurrence rate is significant in American-Atlantic-African, while an anomaly during boreal autumn of the highest S4 max > 0.125 occurrence rate in the Pacific of all seasons and sectors is found. The comparisons of different LT, seasons, and longitudinal sectors are analyzed and discussed in this study, to improve our understanding of the relation between S4 and the generation mechanism of EPBs during solar minimum.