# Advances in Ionospheric Space Weather by Using FORMOSAT-7/COSMIC-2 GNSS Radio Occultations
## 4 Near-Real-Time Global Plasma Bubble Monitoring
### Equatorial and Low-Latitude Ionospheric GNSS L-Band S4 Scintillation  
The F7/C2 radio occultation scintillation is recorded in both 1 and 10 s temporal resolutions (5-10 km and 10-15 km in altitude, respectively). It is calculated by receiving the L1-band (1.5 GHz) CA code of the GPS and GLONASS satellite systems. The F7/C2 provides more than 5000 RO S4-index vertical profiles per day, uniformly observing the mid- and low-latitude (between 40\({}^{\circ}\) N to 40\({}^{\circ}\) S) ionosphere (50 to 550 km in altitude) of the globe every hour. The RO S4-index is considered as one of the indicators of the equatorial plasma bubble (EPB) in the nighttime ionosphere. Therefore, by utilizing the F7/C2 RO S4 data, it is possible to monitor global EPB near-real-time occurrence. Figure 6 displays the distribution of nighttime intense scintillation (S4-index \(>\) 0.5) on 1 January (DOY001) 2022. The occurrence of S4 \(>\) 0.5 appeared dominant in between 0\({}^{\circ}\) E and 60\({}^{\circ}\) W. The occurrence pattern in the longitude-altitude intersection of the geomagnetic equator (the rear diagram) shows both west and east-tilted stripes, indicating the coexistence of C-shape and reverse C-shape EPBs within the longitude sector. In the latitude-altitude intersection of 20\({}^{\circ}\) W longitude (the side diagram), the asymmetry double-peak structure at 15\({}^{\circ}\) N and 15\({}^{\circ}\) S displays the conjugacy of the EPB across the geomagnetic equator. The EPB conjugate pattern can also be seen in the horizontal longitude-latitude diagram of 300 km altitude (the bottom diagram). The F7/C2 S4-index is employed to construct a global EPB occurrence database, which monitors the day-to-day variability of the initiating hour and the total duration time of this particular phenomenon. Figure 7 displays the initiating time and the overall duration of the EPB in low latitudes (between 30\({}^{\circ}\) N and 30\({}^{\circ}\) S) since the launch of the F7/C2. The results showed that EPBs frequently appeared from 20\({}^{\circ}\) W to 80\({}^{\circ}\) W during September and March. The EPBs became scattered worldwide in early August until the end of September, frequently occurred over 0-60\({}^{\circ}\) W during September-March, started scattering worldwide from February to April, and yielded few signatures around 0\({}^{\circ}\) and \(\pm\)180\({}^{\circ}\) longitude during March-September. EPBs mainly appeared between 1800 and 2300 LT. It was found that the EPBs tended to appear earlier and yield a longer duration during the higher solar activity period such as in 2021. Nevertheless, Figure 7 demonstrates that the F7/C2 RO observations can be used to monitor global EPBs in near-real-time. Figure 6: The occurrence of intense S4-index within one night. The color maps indicate the occurrence of intense S4 (red solid dots) in latitudinal (near diagram), longitudinal (side diagram), and altitudinal intersections (bottom diagram) during 2000 LT to 0200 LT of 2022.001 to 2022.002. The longitudinal and seasonal variations of S4 in Figure 7 agree with those reported by previous in situ measurements. Note that earlier ground-based scintillation measurements showed similarity in the occurrence patterns of stronger S4 with the EPB observations by the Defense Meteorological Satellite Program (DMSP) [109] and Communication/Navigation Outage Forecast System (C/NOFS) [110], suggesting the correspondence between stronger S4 regions and ionospheric irregularities. The solar cycle and seasonal distribution of EPBs revealed in Figure 7 more-or-less agree with those reported in DMSP observations [111; 112; 113]. The patterns also show a good agreement with the results from using C/NFOS measurements [114]. [PERSON] et al. [70] noted that the longitudinal variation revealed by F7/C2 S4 better agrees with that of the EPB occurrence in C/NFOS measurements than in DMSP in solar minimum conditions owing to the higher orbit altitude of the latter.