Analysis of Solar Interplanetary Propagation of Space Weather Events in May 2024

A variety of observations are employed to conduct a preliminary analysis of the propagation in solar-interplanetary space of seven earth-directed full-halo Coronal Mass Ejections (CME) originating from the solar Active Region (AR) 13664 from 8 to 11 May 2024. These seven CME can be divided into two groups. The first group consists of four CME that occurred during the period from 05:36 UT on 8 May to 09:24 UT on 9 May, and the second group consists of three CME that occurred during the period from 18:52 UT on 9 May to 01:36 UT on 11 May. We utilize the heliospheric imager on the Solar Terrestrial Relations Observatory A (STEREO A/HI) to observe and track the time-elongation relationships of the high density regions corresponding to these two groups of CME, and apply the fixed Φ-angle fitting method and the harmonic mean fitting method to calculate the most probable propagation directions and average radial velocities of these two groups of CME. The results show that the high-density regions associated with these two groups of CME are respectively overlapped in the field of view of STEREO A/HI. The minimum differences between the two group CME’ arrival times near the Earth’s orbit calculated from the fitting radial velocities and the actual start times observed in situ by the WIND spacecraft are 0.5 hours and 3 hours respectively. These results indicate that during the solar-terrestrial propagation of these two groups of CME, the fast CME behind catch up with the slower CME ahead, thus, the two groups of CME form two complex ejecta and generate the extremely intense geomagnetic storm.