Comparison of geomagnetic activity in solar cycle 12 and 13 with that in cycle 23 and 24.

This study compares the geomagnetic activity observed during the last two secular solar activity maxima: solar cycles 12 and 13,  and 23 and 24, respectively, highlighting the differing patterns of dual and single maxima. In sunspot cycles 12 and 13, we observe a distinct dual-maximum pattern in geomagnetic activity. This pattern contrasts sharply with the singular peaks evident in sunspot cycles 23 and 24. As is well known, the dual peaks in the geomagnetic activity during a sunspot cycle result from the action of two different geoeffective manifestations of solar activity. The peak around sunspot maximum is driven by the Coronal Mass Ejections (CMEs) which are maximium in number and intensity in sunspot maximum. The second peak is due to high-speed solar wind streams (HSS’s) originating from extended coronal holes which maximize during the sunspot declining phase.

This well studied picture is observed during the secular solar minimum between the 19^th and 20^th centuries (sunspot cycles 12 and 13). In contrast, sunspot cycles 23 and 24 in the minimum between the 20^th and 21^st centuries present a different scenario. Despite reaching sunspot maxima, these cycles did not witness corresponding peaks in geomagnetic activity. Our research focuses on unraveling the reasons behind the absence of a geomagnetic peak concurrent with the solar activity maxima in these latter cycles