# Advances in Ionospheric Space Weather by Using FORMOSAT-7/COSMIC-2 GNSS Radio Occultations
## 1 Introduction
[60] provided a detailed overview of such results, highlighting how the F3/C observations contributed to advancing the theoretical understanding of the evolution of the equatorial ionization anomaly (EIA), leading to the identification of new features such as plasma caves and plasma depletion bays, throwing light on the complex processes of coupling from the lower atmosphere that influences the electron density modulations in the ionosphere and new aspects of middle-latitude trough as well as mid-latitude summer nighttime anomalies. They also illustrated the application of F3/C measurements in examining ionospheric signatures induced by seismic and tsunami waves and earthquake precursors, as well as elaborated the global ionosphere specification (GIS) 3D electron density profiles constructed by using RO slant total electron content (TEC) measurements [61; 62]. Note that, despite having 2000-3000 daily occultations, most of such investigations had to rely on average electron densities by combining observations over several days and within relatively larger longitude and latitude grids and time intervals. After such dedicated service lasting about 14 years, far exceeding the expected mission lifetime, which saw more than 4.6 million RO profiles, the F3/C mission was officially decommissioned in May 2020. A follow-up mission named FORMOSAT-7 /COSMIC-2 (F7/C2) has already been launched on 25 June 2019, which also consists of a cluster of six satellites identical to that of the F3/C, circumnavigating the Earth with a period of about 97 min from low-inclination (24\({}^{\circ}\)) orbits at an altitude of \(\sim\)550 km [63]. The Tri-GNSS radio occultation system (TGRS), the main mission payload of F7/C2, receives the refracted signals from GNSS (global navigation satellite system) satellites, including GPS, GLONASS, and Galileo systems, providing many more soundings than its predecessor. This results in, within \(\pm\)35\({}^{\circ}\) latitudes, the daily ionospheric RO profiles of F7/C2 being about four times more than those of F3/C, which allows scientists to examine the equatorial and low-latitude ionosphere with higher temporal and spatial resolutions. The signal quality is also improved through ensuring higher SNR by employing digital beamforming. Instead of the patched antenna arrays of F3/C, the F7/C2 uses advanced phase antenna arrays produced using 3D printing technology for the first time in space applications. The F7/C2 configuration provides approximately 4000 occultations per day, with unprecedented observations facilitating a better understanding of the structures and electrodynamics of the equatorial and low-latitude ionosphere, as well as opening a new chapter for the ionospheric weather forecast. [PERSON] et al. [64] performed the early validation of the F7/C2 electron density profiles and GIS by comparing with manually scaled F-region peak density and peak height from the Digisonde network, yielding correlations in the range 0.86-0.9. Furthermore, [PERSON] et al. [65] carried out a detailed validation and investigation of the retrieved profiles, evaluating the reliability of the measurements and their suitability for ionospheric research and applications. The early orbital period of F7/C2, when the satellites were clustered together, provided information about ionosphere variations in finer temporal and spatial scales [66]. The F7/C2 measurements were used to investigate the role of atmosphere-ionosphere coupling in contributing to the day-to-day ionospheric variability [67], and in particular, to examine the temporal characteristics and 3D features of the electron density modulations during sudden stratosphere warming (SSW) [68]. The observations have also been used to investigate global ionosphere responses during minor magnetic storms [64; 69]. In addition, the S4 scintillation index derived by using the F7/C2 measurements has been shown to be a promising data product for near real-time monitoring of equatorial plasma irregularities [70].