## 3 Results
### Seasonal Variations of IBIs at the Altitudes of Swarm Satellites in Both Hemispheres  
Figure 7a-c illustrate the number of IBIs with respect to months at the altitudes of Swarm A, B, and C from top to bottom. The numbers of IBIs in the northern and southern hemispheres are marked in magenta and black bars respectively. In both hemispheres, the numbers of IBIs in the months around equinoxes are always larger than the number of IBIs in the summer and winter months. This seasonal variation of the occurrence rate of IBIs is independent of the altitude of Swarm satellites. It is worth noting that we could not make a seasonal variation of the number of IBIs for each type of geomagnetic storm because of the limited number of super and intense storms. This limited number of storms confined the appearance of IBIs within two months during super storms and five months during intense storms as indicated in Table 2. Thereby, the seasonal variations of IBIs during different types of geomagnetic storms are suggested to be investigated in further studies. The number of IBIs in the northern hemispheric summer is larger than in the southern  
Figure 6: The duration time of IBIs with respect to the LT for (**a**) different types of geomagnetic storms and (**b**) the altitudes of the three satellites.  
hemisphere. This large occurrence could be attributed to the large electron that develops steeper \(\
abla_{n}\) according to Equation (1).  
Figure 7d is a contour map of the local time with respect to months for the number of IBIs observed during all types of storms. It shows two maxima of the numbers of IBIs within months 9-11. The first maximum is located within 20:00 LT and the other within 22:00 LT and the minimum number of IBIs is within 21:00 LT. In contrast, months 1-4 have an enhancement in the number of IBIs within 21:00 LT. In the June solstice, there are two small peaks of IBI occurrence, the first around 21:00 LT and the other around 23:00 LT.  
Figure 8 shows the seasonal variations of IBIs observed during sunset (17:00-21:00) and pre-midnight (21:00-24:00) local times. IBIs observed by Swarm A, B, and C are marked in red, blue, and cyan colors, respectively. The size of the circle from small to large corresponds to the storm level from moderate to super. The most remarkable points here are, first, the majority of IBIs are observed within the pre-midnight period in all seasons, second, the absence of IBIs during winter months during sunset (local times). The absence of super storm IBIs during the winter months is attributed to the only two super storms that occurred during March and June months. The occurrence of super storm IBIs increases within the pre-midnight period during summer months and sunset during equinoxes. The low occurrence of super EPBs in comparison with moderate EPBs during  
Figure 7: The number of IBIs observed in each month in the northern and southern hemisphere in magenta and black bars, respectively, at the altitudes of (**a**) Swarm A, (**b**) Swarm B, and (**c**) Swarm C. (**d**) a contour map of the local time with respect to months for the number of IBIs.  
summer months within the sunset is in agreement with the authors of [53] who found that the number of post-sunset EPBs during quiet periods is larger than those observed during disturbed periods. This low occurrence of super storm IBIs during summer months (sunset) is reversed in local time during equinoxes, which is a novel feature of IBIs in our analysis. The absence of sunset IBIs during winter months could be attributed to the trans\(-\)equatorial wind that suppresses the occurrence of EPBs in the winter hemisphere as reported in previous studies, but confirming this suggestion needs further investigation.