## 4 Discussion
Further studies could distinguish the altitudinal behavior of IBIs with respect to the DDEF, ring current injection, and IMF Bz. The duration time of IBIs during super, intense, and moderate geomagnetic storms is independent of the type of storm. It also has no correlation with the altitude of the satellite as shown in Figure 6a,b. The duration time of IBIs is only larger from sunset to midnight and independent of the type of the geomagnetic storm and the altitude of the satellite, as it demonstrates a random distribution during different types of geomagnetic storms. It also becomes very large around the SAA region (not shown). According tothis observation, if the electric field strength is the main controller in the duration time (Spatial scale) of IBIs, we would find a high correlation between the duration time and the type of the geomagnetic storm level and an inverse relationship between the duration time and the altitude. Because the large electric field strength raises plasma into higher altitudes (orbits of Swarm B) as obtained in Figures 3 and 5, subsequently low altitudinal ionospheric regions would persist degraded from plasma for longer times than those at higher altitudes especially during super storms. Therefore, this result suggests that the electric field strength has an insignificant contribution to the duration time of IBIs. The enhancement of the duration time of IBIs within the dusk side over the SAA region could be interpreted in terms of the high gradient in the electron density and the depression in the Earth's magnetic field. These are the main factors that could control the scale size (duration time) of the IBI event. A large occurrence of IBIs is recorded within equinox months (February to April and September to November) is shown in Figure 7, which is consistent with previous studies in [61; 65] and references therein. It could be interpreted in terms of the enhanced thermospheric zonal wind during equinoxes [67]. This wind motivates the vertical Pedersen currents that can polarize the initial density disturbance into an unstable mode to trigger plasma bubbles [68]. The low occurrence of IBIs during summer months in both hemispheres is due to the trans\(-\)equatorial wind which suppresses the growth rate of the R\(-\)T instability [62]. Figure 7a-c confirm that seasonal variations of IBIs during the three types of storms recorded in Table 2 are consistent with the general trend of the seasonal occurrence of IBIs reported in [65]. The trans\(-\)equatorial wind may cause a reduction in the local conductivity on the upwind side (summer hemisphere) where the layer is raised and cause an increase in the local conductivity on the downwind side (winter hemisphere) where the layer is lowered. Subsequently, the instabilities in density irregularities near the bubble boundaries may be suppressed in the winter due to the shorted polarization electric field arising from the high conductivity. This might contribute to the slightly lower occurrence rate of the irregularities in the winter hemisphere than the summer hemisphere as shown in Figure 7a-c. The enhanced occurrence of IBIs after sunset times is attributed to the low flux tube integrated conductivity at low magnetic latitudes, where the magnetic field lines are aligned with the terminator [16; 69]. The double small peaks of the IBI occurrence during June solstice around 21:00 and 23:00 are similar to those presented in Figure 6b in [65], but the large double peaks within months 9-12 are different from the single equinoxes' occurrence EPBs peak presented in [65]. The enhancement of super storm IBIs during summer months within the pre-midnight and sunset periods during equinoxes is an interesting observation and needs further investigation.