Investigation of the Geoeffectiveness of Disk-Centre Full-Halo Coronal Mass Ejections

Abstract

We studied the occurrence and characteristics of geomagnetic storms associated with disk-centre full-halo coronal mass ejections (DC-FH-CMEs). Such coronal mass ejections (CMEs) can be considered as the most plausible cause of geomagnetic storms. We selected front-side full-halo coronal mass ejections detected by the Large Angle and Spectrometric Coronagraph onboard the Solar and Heliospheric Observatory (SOHO/LASCO) from the beginning of 1996 till the end of 2015 with source locations between solar longitudes E10 and W10 and latitudes N20 and S20. The number of selected CMEs was 66 of which 33 (50%) were deduced to be the cause of 30 geomagnetic storms with $\mathrm{Dst} \leq- 50~\mbox{nT}$ . Of the 30 geomagnetic storms, 26 were associated with single disk-centre full-halo CMEs, while four storms were associated, in addition to at least one disk-centre full-halo CME, also with other halo or wide CMEs from the same active region. Thirteen of the 66 CMEs (20%) were associated with 13 storms with $-100~\mbox{nT} < \mbox{Dst} \leq- 50~\mbox{nT}$ , and 20 (30%) were associated with 17 storms with $\mbox{Dst}\leq- 100~\mbox{nT}$ . We investigated the distributions and average values of parameters describing the DC-FH-CMEs and their interplanetary counterparts encountering Earth. These parameters included the CME sky-plane speed and direction parameter, associated solar soft X-ray flux, interplanetary magnetic field strength, $B_{t}$ , southward component of the interplanetary magnetic field, $B_{s}$ , solar wind speed, $V_{sw}$ , and the $y$ -component of the solar wind electric field, $E_{y}$ . We found only a weak correlation between the Dst of the geomagnetic storms associated with DC-FH-CMEs and the CME sky-plane speed and the CME direction parameter, while the correlation was strong between the Dst and all the solar wind parameters ( $B_{t}$ , $B_{s}$ , $V_{sw}$ , $E_{y}$ ) measured at 1 AU. We investigated the dependences of the properties of DC-FH-CMEs and the associated geomagnetic storms on different phases of solar cycles and the differences between Solar Cycles 23 and 24. In the rise phase of Solar Cycle 23 (SC23), five out of eight DC-FH-CMEs were geoeffective ( $\mbox{Dst} \leq- 50~\mbox{nT}$ ). In the corresponding phase of SC24, only four DC-FH-CMEs were observed, three of which were nongeoeffective ( $\mbox{Dst} > - 50~\mbox{nT}$ ). The largest number of DC-FH-CMEs occurred at the maximum phases of the cycles (21 and 17, respectively). Most of the storms with $\mbox{Dst}\leq- 100~\mbox{nT}$ occurred at or close to the maximum phases of the cycles. When comparing the storms during epochs of corresponding lengths in Solar Cycles 23 and 24, we found that during the first 85 months of Cycle 23 the geoeffectiveness rate of the disk-centre full-halo CMEs was 58% with an average minimum value of the Dst index of $- 146~\mbox{nT}$ . During the corresponding epoch of Cycle 24, only 35% of the disk-centre full-halo CMEs were geoeffective with an average value of Dst of $- 97~\mbox{nT}$ .