Abstract

The solar sources of 884 geomagnetic storms have been studied for the solar cycles 23 and 24 (1996-2019), regardless of their size ranges; using the Kp index and the NOAA G criteria (minor to extreme storms). It claims from our investigation that fast solar wind streams (HSSWs) is the main factor of small (G1) and medium (G2) storms and occur mostly on the descending phase of the solar cycle. Fast solar wind has contributed to about 59% of G1 storms; 50% of G2; 29% G3; and 10% G4 storm. Large storms (G3 to G5) are the effects of coronal mass ejections (CMEs) and they are observed mainly during the maximum and the descending phases of the solar cycle. About 10% of G1 storms, 26% of G2 storms, 59% of G3 (strong) storms, 87% of G4 (severe) storms, and 100% of G5 (extreme) storms were the effect of CMEs. Magnetic clouds contributed 11% of G1 storms, 15% of G2 storms, 9% of G3 storms, and 3% of G4 storms. A comparative statistical occurrence shows that the number of storms decreased during solar cycle 24 when compared with the solar cycle 23. These results showed that the magnetospheric energy transfer decreased in solar cycle 24 and that the magnetosphere was under the influence of intense solar magnetic fields in solar cycle 23. The phenomenon observed in these investigations highlight a drop in solar plasma geoeffectiveness since the long minimum that followed the solar cycle 23.

Key words: Magnetic storms, coronal mass ejections (CMEs), high speed solar winds stream (HSSWs), magnetic clouds (MCs), solar cycle.