Study of the propagation, in situ signatures, and geoeffectiveness of shear-induced coronal mass ejections in different solar winds

Abstract

Aims. Our goal is to propagate multiple eruptions –obtained through numerical simulations performed in a previous study– to 1 AU and to analyse the effects of different background solar winds on their dynamics and structure at Earth. We also aim to improve the understanding of why some consecutive eruptions do not result in the expected geoeffectiveness, and how a secondary coronal mass ejection (CME) can affect the configuration of the preceding one. Methods. Using the 2.5D magnetohydrodynamics package of the code MPI-AMRVAC, we numerically modelled consecutive CMEs inserted in two different solar winds by imposing shearing motions onto the inner boundary, which in our case represents the low corona. In one of the simulations, the secondary CME was a stealth ejecta resulting from the reconfiguration of the coronal field. The initial magnetic configuration depicts a triple arcade structure shifted southward, and embedded into a bimodal solar wind. We triggered eruptions by imposing shearing motions along the southernmost polarity inversion line, and the computational mesh tracks them via a refinement method that applies to current-carrying structures, and is continuously adapted throughout the simulations. We also compared the signatures of some of our eruptions with those of a multiple CME event that occurred in September 2009 using data from spacecraft around Mercury and Earth. Furthermore, we computed and analysed the Dst index for all the simulations performed. Results. The observed event fits well at 1 AU with two of our simulations, one with a stealth CME and the other without. This highlights the difficulty of attempting to use in situ observations to distinguish whether or not the second eruption was stealthy, because of the processes the flux ropes undergo during their propagation in the interplanetary space. We simulate the CMEs propagated in two different solar winds, one slow and another faster one. In the first case, plasma blobs arise in the trail of eruptions. The faster solar wind simulations create no plasma blobs in the aftermath of the eruptions, and therefore we interpret them as possible indicators of the initial magnetic configuration, which changes along with the background wind. Interestingly, the Dst computation results in a reduced geoeffectiveness in the case of consecutive CMEs when the flux ropes arrive with a leading positive Bz. When the Bz component is reversed, the geoeffectiveness increases, meaning that the magnetic reconnections with the trailing blobs and eruptions strongly affect the impact of the arriving interplanetary CME.