Magnetosphere–ionosphere response to the 21 and 25 June 2015 coronal mass ejections

Abstract. Using a coupled EUHFORIA–Gorgon-Space modelling chain, we simulate the magnetosphere–ionosphere coupled response to two coronal mass ejections (CMEs) that impacted Earth on 23 and 28 June 2015. The first CME (CME1), launched on 21 June, triggered a major geomagnetic storm (Kp = 8), driving strong magnetosphere–ionosphere coupling characterised by a cross-polar cap potential of 160 kV and intense field-aligned currents exceeding 23 MA, key indicators of energy transfer from the solar wind into the high-latitude ionosphere. In contrast, the faster CME2 (launched on 25 June) produced only a weak disturbance (Kp ≈ 2) due to the absence of a prolonged southward interplanetary magnetic field (IMF), resulting in minimal magnetospheric driving and ionospheric feedback. These results validate an end-to-end space-weather forecasting framework and demonstrate that CME geoeffectiveness is governed primarily by the IMF orientation and reconnection-driven magnetosphere–ionosphere energy coupling, rather than by kinematic properties such as speed alone.