Radial Evolution of Interplanetary Coronal Mass Ejections and Change of Their Geo-effectiveness Due to Erosion

Magnetic ejecta (ME) characterized by large-scale smoothly-rotating magnetic field lines inside interplanetary coronal mass ejections (ICMEs) may erode while interacting with the surrounding ambient solar wind plasma in the heliosphere. Erosion may occur while ICME-surrounding solar wind structures are in favorable conditions leading to magnetic reconnection with MEs. Erosion may peel off the outer layers of ME eventually leading to changes in their structures and magnetic properties. In this study, we analyze the erosion of three ICME events observed by very rare radial alignments of multiple spacecraft, where the spacecraft were within 3.5 degrees of angular separations. The three events were observed by pairs of spacecraft: (1) Parker Solar Probe (0.53 au) and Wind (0.997 au) on September 2023, (2) Solar Orbiter (0.85 au) and Wind (0.98 au) on November 2021, and (3) STEREO-A (0.95 au) and Wind (1.005 au) on August 2023. Analyzing the radial evolution of the magnetic, ion and supra-thermal electron properties and Alfvenicity inside the MEs, and reconnection exhausts at their boundaries, we assess the impact of erosion on the structures of ME and their geo-effectiveness. Thus, taking the opportunity of such rare spacecraft alignments, we comment on how erosion may impact ICME radial evolution and may lead space weather prediction operations to be more challenging in the heliosphere.