Abstract
The angular width of coronal mass ejections (CMEs) and the variations of CME properties for various crossings through the structure remain insufficiently studied and inadequately understood, primarily due to the rarity of multispacecraft measurements. From 2022 January to 2023 August, STEREO-A was in relative proximity to the Sun–Earth first Lagrangian (L1) point, with the STEREO-A–L1 angular separation reducing from 35∘ to 0∘, corresponding to a time with an increasing activity of solar cycle 25 approaching its maximum. This provides a unique time period to obtain multispacecraft measurements of CMEs and to analyze their properties as observed by Wind/ACE and STEREO-A. Among 49 total CMEs measured by either spacecraft over the 20 months, only 15 were simultaneously detected at both spacecraft, indicating that only 31% of CMEs impacted both within a longitudinal separation of 0∘–35∘. While 80%–100% of CMEs were observed by both spacecraft within 10∘, this percentage rapidly dropped to approximately 30% beyond 10∘, and near 30∘, it fell further to 10%. These findings suggest that the average CME angular width near 1 au is likely between 20∘and 35∘, smaller than previously suggested. Furthermore, the analysis of these 15 events reveals that average CME properties like magnetic field strength and proton speed are largely consistent regardless of angular separation. However, correlations and rms error analyses highlight significant variability in CME properties even within separations of 10∘–20∘, when examining their internal variations in detail. This study raises numerous questions about our knowledge of CME properties.
