## 4 Discussion  
As shown in the previous section, we have introduced our observations of the morphology of EPB events recorded by Swarm satellites during different types of geomagnetic storms recorded from 2014 to 2020. We have investigated 59 geomagnetic storms (2 super, 7 intense, and 50 moderate storms) under our classification set in Section 2. A list of 831 IBI events was recorded by the Swarm constellation during all storms. Figure 2, shows that most IBIs are located within \(\pm 20^{\circ}\) geomagnetic latitudes and between \(90^{\circ}\) W and \(20^{\circ}\) E corresponding to the location of the SAA. The plasma drift velocity \(v_{z}\) is related to the Earth's magnetic and electric fields in the following form (\(v_{z}\propto\frac{F}{B}\)). Therefore, within the dusk sector, the eastward electric field is greatest and subsequently, the R - T irregularities increase rapidly. The number of IBIs in the northern hemisphere is always larger than those in the southern hemisphere. The north\(-\)south hemispheric asymmetry of the IBIs in summer months could be attributed to the large electron density which develops steeper \(\
abla_{n}\) according to Equation (1) [17; 46]. Also, it is worth noting that the large electron density during equinoxes [55] is considered the main reason behind the large equinoctial IBIs. Also, the authors of [53] proposed that the increase in the background plasma density at the topside F region improves the EPB development in two ways: by enhancing the growth of EPD along the flux tube or by maintaining EPB rising upward. According to individual storms listed in Table 2, the occurrence rate of IBIs is not necessarily increasing with the storm level, as several moderate geomagnetic storms recorded a large number of IBIs in comparison with super storms. These results are in agreement with the authors of [62] who found that the occurrence of EPBs is suppressed or enhanced for individual storm cases. Generally, we have found a large occurrence of IBIs after sunset times. One of the most significant creation techniques of plasma irregularities within this time is the prereversal enhancement (PRE) eastward electric field [64]. The PRE can supply a suitable circumstance for evolving the R-T instability and raising the equatorial upward drift velocity. The probability of observing EPB at high altitudes (the orbit of Swarm B) increases with the increase in the geomagnetic storm level as shown in Figures 3 and 5. The altitudinal analysis of EPBs presented by the authors of [65] found that the post-midnight EPBs extend to higher altitudes over the African and American sectors. According to Figure 4, these regions are characterized by low magnetic field strength; therefore, the growth rate of EPBs according to Equation (1) is very large. Our analysis shows that, not only does the occurrence rate of IBIs increase over the African and American regions but also, the probability of observing IBIs at high altitudes (orbit of Swarm B) increases during super storms, as shown in Figure 5a. Regardless, the author of [66] found a significant reduction in the height of the F layer within the evening hours and significant enhancement in the post-midnight period of the April 24, 2012 magnetic storm, suppression in the number of IBIs was observed during these local times. They attributed this suppression to the westward electric field associated with the DDEF or other factors such as injection of the ring current and the IMF Bz. Therefore, the large occurrence of IBIs at high altitudes during super storms in our analysis could be interpreted in terms of the enhanced eastward electric field. The enhanced strength of the electric field forces plasma to move into higher altitudes and increases the probability of observing IBIs at higher altitudes especially within the post-sunset period. This suggestion is acceptable only in case of no injection to the ring current and if the IMF Bz is positive.