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

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 (MHD) package of the code MPI-AMRVAC, we numerically modeled consecutive CMEs inserted in two different solar winds by imposing shearing motions onto the inner boundary. The initial magnetic configuration depicts a triple arcade structure shifted southward, and embedded into a bimodal solar wind. We compared our simulated signatures with those of a multiple CME event in Sept 2009 using data from spacecraft around Mercury and Earth. 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. Only in the first case, plasma blobs arise in the trail of eruptions. 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.
Comment: 15 pages, 13 figures