## 3 Results and Discussion  
### Post-Midnight EPBs from CSES-01 Observations  
Table 1 summarizes the number of EPBs automatically detected from 1 January 2019 to 31 May 2024 by both the LP and the EFD algorithms, together with the number of semiorbits in which at least one EPB was detected. It is worth noting that the two algorithms do not detect the same number of ionospheric irregularities. This is essentially due to the differences between LP and EFD measurements, which, as described in Sections 2.2 and 2.3, resulted in the need to adopt different proxies and independent thresholds to optimize the automatic detection. The higher number of irregularities detected by the LP algorithm compared with EFD is mainly due to its ability to count even smaller irregularities (see points 2 and 3 in Section 2.2), which usually occur inside a plasma bubble (see, e.g., [69] and reference therein). Furthermore, the EFD saturation effect, which could occur in correspondence with intense depletions (\(<\)10\({}^{8}\) m\({}^{-3}\); see [70]), makes the electric field measurement less reliable to reveal the presence of electric field fluctuations in correspondence with strong EPBs. By comparing the irregularities identified by EFD with those identified by LP, it is observed that the semiorbits of the common detections (last column in Table 1) represent \(\sim\)41.3% of the entire LP dataset. Based on the above arguments, one would expect such a percentage to be much higher (around 80% accounting for algorithms' performance), since by design, EFD detections should be a subset of LP detections. This apparent discrepancy is explained by the fact that the estimated rate of false positive detections of the EFD algorithm is \(\sim\)57% (see Section 2.3), while for the LP algorithm, it is less than 10%. Therefore, out of the 1598 semiorbits of positive detection reported for EFD, only half are true detections, which correspond roughly to the number of common semiorbits. Figure 5: From top to bottom: electron density from LP data, electric field amplitude from EFD-ELF data, and activity proxy V\({}^{\text{max}}\) for a false negative (**left**) and false positive (**right**) detection of the EFD algorithm. As discussed in the previous Section (also visible in Figure 5), the proxy used for the EPBs detection using EFD data is sensitive to electric field variations, eventually associated with other physical phenomena (such as whistlers). In any case, common detection from the EFD and LP algorithms allows for investigating the electric field dynamics of EPBs. In addition, the false positive detections (identified by the combined use of the two algorithms) can be exploited to investigate other physical phenomena. By investigating the latitudinal extension and the latitudinal occurrence (see Figure 6) of detected irregularities, we found that most of them have an extension within 1000 km (bottom panels) and occur within a narrow band of \(\pm\)20\({}^{\circ}\) of quasi-dipole magnetic latitude (top panels). These results suggest a good agreement between the two algorithms, highlighting their complementarity in identifying these types of ionospheric irregularities. The goodness of these results is also confirmed by the monthly EPBs occurrence distributions detected by the two algorithms, as shown in Figure 7. As visible by comparing left and right panels, showing LP (left) and EFD (right) EPBs occurrences, respectively, both algorithms detected the largest number of equatorial irregularities during the solstice months. This result agrees well with previous studies, which reported an increased occurrence of post-midnight EPBs during solstice periods of low solar activity (e.g., [71; 72; 73; 74]). In particular, [PERSON] et al. [75], analyzing ion density perturbations based on measurements made by the Communication/Navigation Outage Forecasting System (C/NOFS) satellite, pointed out that the maximum in the occurrence rate of irregularities across midnight into the post-midnight hours takes place during the June and December solstices.