How Different Are the SolarWind-Interplanetary Conditions and the Consequent Geomagnetic Activity During the Ascending and Early Descending Phases of the Solar Cycles 23 and 24?

摘要

The current work investigates the possible solar wind-interplanetary (SW-IP) drivers of geomagnetic storms during the longest period (ascending to early descending phases) of the ongoing solar cycle (24). We present a comparative analysis between the two consecutive solar cycles (SCs) 23 and 24. Both the cycles exhibited dual peak feature as observed in the smoothed sunspot numbers SSN_(smoothed). For both the cycles, second peak in the SSN_(smoothed) is higher than the first one as exhibited in the revised SSN_(smoothed) version. During the entire interval between the ascending to early descending phases (December 2008 to December 2016) of SC-24, the southward directed Bz and the dawn-dusk electric field (Ey) were consistently weaker as compared to that during similar interval of SC-23 (May 1996 to July 2004). The geomagnetic field response represented by Dst index concurrently exhibited similar variation patterns during both the periods. A striking reduction in the intense storm occurrence rate by ~75% was observed during the considered period of the current solar cycle in comparison to the previous cycle. However, moderate storm occurrence was reduced only by 32% in SC-24 as compared to SC-23, which could be attributed to the dominance of corotating interaction regions during SC-24. No significant difference is found between the intense storm rates around the vernal and autumnal equinoxes in cycle 24, whereas distinct autumnal equinoctial dominance is evident for cycle 23. Further, within each cycle, there is no significant difference in the moderate storm rates around vernal and autumnal equinoxes.