Relationships between Interplanetary Coronal Mass Ejection Characteristics and Geoeffectiveness in the Declining Phase of Solar Cycles 23 and 24

In this paper, we have examined the relationships between the characteristics of interplanetary coronal mass ejections (ICMEs) and geoeffectiveness in the declining phase of Solar Cycles 23 and 24. We discuss the results in comparison with those of the rising phase. Major results of this study are as follows: The ICMEs in the declining phase of Cycle 23 have generated higher storm strength than those in Cycle 24. The mean storm strength of the sheath and ICME for each cycle in the declining phase is greater than in the rising phase. This indicates that the declining phase is more geoeffective than the rising phase. Cycle 24 events seem to be slightly more geoeffective towards the second half of the cycle even though the cycle is weak in the rising phase. The mean radial size of ICMEs is ∼ 0.36 AU in Cycle 23 and ∼ 0.32 AU in Cycle 24. Around 25