Observation and Modeling of the 2011 May 28 Geo-Effective Event

Abstract

We present a combined observational and modeling study of a geo-effective event on 2011 May 28, which produced a symmetric horizontal component index (SYM-H) index of −80 nT. The event occurred when active regions were bordered by a large coronal hole, potentially influencing the behavior of eruptive structures. We analyze magnetogram and extreme ultraviolet (EUV) images and find that this event involved two filament eruptions 8 hours apart from two different active regions closed to each other. Then, we track their coronal mass ejection (CME) counterparts using coronagraph images. We analyze plasma, magnetic field, particle energies and the SYM-H to find their relationship to the CMEs and the high-speed streams (HSS). The HSS interval is marked by enhanced particle energies and thermal speeds, with reduced ionic charge states and elemental abundance ratios, whereas the CME intervals exhibit the opposite behavior, emphasizing their distinct plasma characteristics. We reconstruct 3D magnetic field configurations for the active regions and assessed flux rope stability. We find that the presence of a nearby coronal hole makes flux ropes unstable at lower axial flux values, approximately three times smaller than in comparable cases without a coronal hole. Using a hydrodynamic (HD) model, constrained by remote sensing, and in situ data, we track the CME/ICME propagation up to 1 au. The model reproduces the overall timing and structure of the transients. Our results suggest that the coronal hole likely influenced CME propagation and may have reduced interactions between the CMEs, with the transients subsequently propagating along the solar wind streams emerging from the coronal hole. This study demonstrates how nearby magnetic structures can affect CME dynamics, which is critical for forecasting Earth-directed solar transients.