the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 30 Jan 2026
"Corotating Interaction Region (CIR)", "Interaction Region", "Stream Interaction Region (SIR)", which term should be used?
Abstract. We discuss the history of quasiperiodic ~27-day recurrent geomagnetic activity and the origin of the names "interaction region", "corotating interaction region" and "stream interaction region". The latter three names have an identical meaning. We recommend the most commonly used name "corotating interaction region" or CIR for sole usage in the literature to avoid confusion.
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Status: open (until 13 Mar 2026)
- RC1: 'Comment on egusphere-2026-5', Anonymous Referee #1, 30 Jan 2026 reply
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RC2: 'Comment on egusphere-2026-5', Anonymous Referee #2, 09 Feb 2026
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The present manuscript comes back on the long-term persisting debate about whether should we say Co-rotating Interaction Region (CIR) or Stream Interaction (SIR) when talking about the overtake of a slow solar wind by a higher speed solar wind stream. Modern convention being to consider CIRs to be a subset of SIRs that persists for several rotations. Retracing the historical consideration of such events is a valuable point of this article. Neverheless, although the authors' recommandation to stick with the term CIR is understandable, the reasons they advance should be further detailed before considering the acceptance of their manuscript.
For instance:
- l.109-114: Although the events that do not recur 27days later do have a poor recurrence, I am not sure they have a poor occurrence in the existing stream interaction region catalogs (Jian et al. (2006), Chi et al. (2018), Nguyen et al. (2025)). Additionally, even if this naming includes so-called "transient and possibly localized stream interactions", these events still share common in-situ patterns when observed at L1 resulting in possible impact for the near-Earth environment. A possible distinction that could also be discussed would stand in the origin of such events, linking their occurrence with coronal hole. The actual denomination however appear as the most inclusive regarding the diversity of such events.
- l.120-132: The event presented in this paragraph is interseting but rather concerns the confusion made between ICMEs and SIRs. Thus, the interest for the debate raised by this manuscript is unclear.
- l.138-139: The authors' point about the possible misinterpretation of the concept of tangential discontinuity is quite interesting and could be a good argument in favor of their opinion. It is however barely mentioned and expanded in the paper.
For these reason, I would recommand the authors to strengthen the arguments in favor of their opinion beofre considering the acceptance of this paper.
Citation: https://doi.org/10.5194/egusphere-2026-5-RC2
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I understand the authors’ concern on the terminology confusions, as some authors use these two terms interchangeably (Waugh and Jardine, 2025). However, I’m not convinced with the authors’ current narratives. According to the modern studies, CIRs (coronating interacting regions) are used as subsets of SIRs (stream interacting regions). Allen et al. (2020) stated, “After a complete solar rotation, the SIR is classified as a corotating interaction region (CIR)”. Richardson (2018) uses “the general term “stream interaction region”, while being aware that some authors (e.g., Jian et al. 2006) use this term to distinguish a stream that is observed on only one solar rotation from a “corotating” interaction region that is seen on more than one rotation.” If the scientific community stops using the term of SIR, how would we call the CIRs that did not persist as long as one solar rotation? It’s straightforward to understand CIRs as a subset of SIRs.