Multi-spacecraft Probing of CME Field Structure at Small Longitudinal Separations

Authors: Brian E. Wood (NRL), Phillip Hess (NRL)

With STEREO-A completing its first orbit around the Sun relative to the Earth on 2023 August 12, the spacecraft has been operating close to Earth in recent years.  Specifically, STEREO-A is within 15 degrees of Earth from 2022 November to 2024 June.  During this period, STEREO-A has been hit by many of the same CMEs that hit Earth, offering an opportunity to study CME field structure with spacecraft separated by small longitudinal separations, providing valuable tests for the flux rope paradigm.  We report on observations of CMEs from 2023 April 21 and 2023 November 28, which hit Earth and STEREO-A on 2023 April 23 and 2023 December 1, with STEREO-A being 10.2 and 6.5 degrees from Earth, respectively.  The latter CME also hits Solar Orbiter, which at the time was 11.4 degrees from Earth at a distance from the Sun of 0.85 AU, probing the opposite side of the CME than STEREO-A relative to Earth.  We perform 3-D morphological reconstructions of the CMEs based on imaging from STEREO-A, SOHO/LASCO, and Solar-Orbiter/SoloHI.  We seek to determine if the flux rope shapes are consistent with the in situ signatures, and the observed spatial variation of those signatures from spacecraft to spacecraft (Wind, STEREO-A, and Solar Orbiter).