## 4 Conclusions  
In this work, the electron density and TEC data in 8 years' measurements from the Swarm constellations are utilized to study the occurrence rate of global ionospheric irregular structures and the phase scintillation in the topside ionosphere. The occurrence patterns are analyzed by season, local time, longitude, latitude, and solar activity. The scintillation mainly presents consistent results with the irregularities at low latitudes, but the scintillation shows many differences from the irregularities at middle latitudes. The main results are summarized as follows:  
1. At low latitudes, the occurrence rate of postmidnight EPIs is generally decreased, except during the June solstice. During the June solstice, a large number of EPIs appear after midnight, resulting in the occurrence rate peaks at around 01:00 LT. The occurrence rate of EPIs displays an increasing trend with the increasing solar activities. The topside ionospheric scintillation shows relatively consistent results with EPIs, while the scintillation occurrence is quite weak during the June solstice. These results indicate that EPIs contribute most of the topside ionospheric scintillation, but the scintillation could also depend on other factors. 2. The midlatitude irregularities mainly occur after midnight, and the occurrence rate is negatively correlated with solar activity and lowest during the equinoxes and highest during the June solstice. The occurrence rate presents hemispheric asymmetry and is higher in the winter hemisphere than in the summer hemisphere during the solstices. During the June solstice, the peak occurrence rate is concentrated in the Pacific sector, whereas during the December solstice, the peak is seen in the American sector. However, the topside ionospheric scintillation shows many differences from the irregularities. The topside ionospheric scintillation has no significant hemispheric asymmetry during the June solstice and is concentrated in the southern hemisphere during the December solstice, which might be related to the background electron density in the topside ionosphere after midnight. The EPIs concentrate more at the altitudes of Swarm A, while the midlatitude irregularities mainly occur at the altitudes of Swarm B. At both low and middle latitudes, topside ionospheric scintillation has a higher occurrence in Swarm A observations, which might be related to the longer integration path of TEC, resulting in more irregularities for the signal to cross. * In addition, there are latitudinal and longitudinal dependences in the global distribution of S4c-based irregularities. However, due to the absence of seasonal dependence, the equivalent scintillation index S4c on the satellite needs further study. Conceptualization, J.K., K.W., J.Z. and X.W. ; methodology, J.Z. and X.W. ; software, K.W., H.S., J.C., X.S. and H.H. ; validation, J.K., J.Z., X.W. and F.H. ; formal analysis, K.W., X.S. and H.H. ; investigation, K.W., X.W. and H.S. ; resources, J.K., K.W., J.Z., X.W. and X.S. ; data curation, K.W., J.C., X.S. and H.H. ; writing--original draft preparation, K.W. and J.Z. ; writing--review and editing, J.K., K.W., J.Z., X.W. and F.H. ; visualization, J.K., K.W., J.Z. and X.W. ; supervision, J.K. and J.Z. ; project administration, J.K. and J.Z. ; funding acquisition, J.K. and J.Z. All authors have read and agreed to the published version of the manuscript.