Statistical Study of the Geoeffectivity of Halo Coronal Mass Ejections Associated with X-Class Flares during Solar Cycles 23 and 24

By analysing a long series of data (1996-2019), we show that solar cycle 23 was more marked by violent solar flares and coronal mass ejections (CMEs) compared to solar cycle 24. In particular, the halo coronal mass ejections associated with X-class flares appear to be among the most energetic events in solar activity given the size of the flares, the speed of the CMEs and the intense geomagnetic storms they produce. Out of eighty-six (86) X-class halo CMEs, thirty-seven (37) or 43% are highly geoeffective; twenty-four (24) or approximately 28% are moderately geoeffective and twenty-five (25) or 29% are not geoeffective. Over the two solar cycles (1996 to 2019), 71% of storms were geoeffective and 29% were not. For solar cycle 23, about 78% of storms were geoeffective, while for solar cycle 24, about 56% were geoeffective. For the statistical study based on speed, 85 halo CMEs associated with X-class flares were selected because the CME of 6 December 2006 has no recorded speed value. For both solar cycles, 75.29% of the halo CMEs associated with X-class flares have a speed greater than 1000 km/s. The study showed that 42.18% of halo (X) CMEs with speeds above 1000 km/s could cause intense geomagnetic disturbances. These results show the contribution (in terms of speed) of each class of halo (X) CMEs to the perturbation of the Earth’s magnetic field. Coronal mass ejections then become one of the key indicators of solar activity, especially as they affect the Earth.