Authors: N. Lugaz (UNH), N. Al-Haddad (UNH), B. Zhuang (UNH), S. Banu (UNH), C. J. Farrugia (UNH), R. M. Winslow (UNH), C. Scolini (ROB), E. E. Davies (Geosphere), C. Möstl (Geosphere), A. B. Galvin (UNH)

We take advantage of STEREO-A angular separation of 20°–60° from the Sun–Earth line from 2020 October to 2022 August, and perform a study to constrain the angular width of magnetic ejecta within CMEs in the ecliptic plane. A key finding is that out of 21 CMEs propagating within 30° of either spacecraft (based on remote-sensing observations), only four impacted both spacecraft and none provided clean magnetic cloud-like signatures at both spacecraft.We conclude that the typical angular width of an ME at 1 au is ∼20°–30°, or 2–3 times less than often assumed and consistent with a 2:1 elliptical cross section of an ellipsoidal ME. We discuss the consequences of this finding for future multi-spacecraft mission designs and for the coherence of CMEs. We then further investigate the 2023 April ME measured by spacecraft at L1 and STEREO-A to discuss the variations of the CME properties for two spacecraft separated by 10° and further discuss CME coherence for this particular event.