Characterisation of in situ signatures of coronal mass ejections interacting with high-speed streams

¹ University of Zagreb, Faculty of Geodesy, Hvar Observatory 10000 Zagreb, Croatia
² Institut de Recherche en Astrophysique et Planétologie (IRAP) 31400 Toulouse, France
³ Centre National d’Etudes Spatiales (CNES) 31400 Toulouse, France
⁴ Institute of Physics, University of Graz Universitätsplatz 5 8010 Graz, Austria

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 2 June 2025
Accepted: 28 December 2025

Abstract

Aims. Interactions between coronal mass ejection (CMEs) and high-speed streams (HSSs) have the capacity to alter their plasma and magnetic field properties. The properties of such interactions are expected to be encoded in the in situ plasma and magnetic field observations. To characterise the properties of these interactions, we aim to analyse the in situ signatures of 28 interplanetary coronal mass ejections (ICMEs) interacting with high-speed streams (HSS) at 1 AU between 2010 and 2018.

Methods. We analysed the ICME velocity profiles, the duration of the sheath and magnetic obstacle (MO), and the distortion of the MO, as well as search for the signatures of the reconnection exhausts. We found twenty events where the ICME was located in front of the HSS and eight where it was behind. Statistical analyses were performed separately for these two classes of interactions.

Results. We find that ICMEs interacting with an HSS generally show distinct speed profiles for cases where an HSS is in front and behind. We find that for HSS in front cases, the formation of the sheath is hindered, and the duration of MO seems to be shorter with a lower average magnetic field magnitude. We find that HSSs catching up to ICMEs tend to compress and accelerate them from the back, whereas HSSs in front of ICMEs do not significantly alter the typical speed expansion profiles. Although we find reconnection exhaust signatures in about 30% events, we do not find significant evidence of the distortion of the internal magnetic structure.

Conclusions. Our results indicate that interaction with an HSS does not significantly influence the ICME internal magnetic structure. However, it might significantly influence its kinematics.