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Did CME 3 and CME 4 physically interact in 3D?

Ascertain whether CME 3, associated with a quiet-Sun filament eruption near AR 13667, and CME 4, associated with AR 13664, physically interacted in three dimensions during their propagation observed by STEREO-A/HI1 on 8 May 2024, rather than merely overlapping along the line of sight.

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Background

Using STEREO-A Heliospheric Imager observations, the authors tracked five CMEs, noting CME 3 was overtaken by CME 4 shortly after entering the HI1 field of view. However, HI1 provides line-of-sight imagery, which can create apparent overlaps without actual interaction in 3D.

The longitudinal separation between the apices of CME 3 and CME 4 is large (about 29°), further complicating the determination of whether a true interaction occurred. Establishing whether these CMEs interacted has implications for understanding CME-CME interactions and their potential impact on geoeffectiveness.

References

However, it is unclear whether the two CMEs physically interact.

— First observations of a geomagnetic superstorm with a sub-L1 monitor (2411.12490 - Weiler et al., 19 Nov 2024) in Solar and Remote Sensing Observations (Section 2)