Halo coronal mass ejections during Solar Cycle 24: reconstruction of the global scenario and geoeffectiveness

Coronal mass ejections (CMEs), in particular Earth-directed ones, are regarded as the main drivers of geomagnetic activity. In this study, we present a statistical analysis of a set of 53 fast (V ≥ 1000 km·s−1) Earth-directed halo CMEs observed by the SOHO/LASCO instrument during the period Jan. 2009–Sep. 2015, and we then use this CME sample to test the forecasting capabilities of a new Sun-to-Earth prediction scheme for the geoeffectiveness of Earth-directed halo CMEs. First, we investigate the CME association with other solar activity features such as solar flares, active regions, and others, by means of multi-instrument observations of the solar magnetic and plasma properties, with the final aim of identifying recurrent peculiar features that can be used as precursors of CME-driven geomagnetic storms. Second, using coronagraphic images to derive the CME kinematical properties at 0.1 AU, we propagate the events to 1 AU by means of 3D global MHD simulations. In particular, we use the WSA-ENLIL+Cone model to reconstruct the propagation and global evolution of each event up to their arrival at Earth, where simulation results are compared with interplanetary CME (ICME) in-situ signatures. We then use simulation outputs upstream of Earth to predict their impact on geospace. By applying the pressure balance condition at the magnetopause and the coupling function proposed by Newell et al. [J Geophys Res: Space Phys 113 (2008)] to link upstream solar wind properties to the global Kp index, we estimate the expected magnetospheric compression and geomagnetic activity level, and compare our predictions with global data records. The analysis indicates that 82% of the fast Earth-directed halo CMEs arrived at Earth within the next 4 days. Almost the totality of them compressed the magnetopause below geosynchronous orbits and triggered a minor or major geomagnetic storm afterwards. Among them, complex sunspot-rich active regions associated with X- and M-class flares are the most favourable configurations from which geoeffective CMEs originate. The analysis of related Solar Energetic Particle (SEP) events shows that 74% of the CMEs associated with major SEPs were geoeffective, i.e. they triggered a minor to intense geomagnetic storm (Kp ≥ 5). Moreover, the SEP production is enhanced in the case of fast and interacting CMEs. In this work we present a first attempt at applying a Sun-to-Earth geoeffectiveness prediction scheme − based on 3D simulations and solar wind-geomagnetic activity coupling functions − to a statistical set of fast Earth-directed, potentially geoeffective halo CMEs. The results of the prediction scheme are promising and in good agreement with the actual data records for geomagnetic activity. However, we point out the need for future studies performing a fine-tuning of the prediction scheme, in particular in terms of the evaluation of the CME input parameters and the modelling of their internal magnetic structure