Case study on the evolution of corotating interaction regions for the “smiley coronal holes”: 0.3 to 1 AU

¹ University of Graz Universitätspl. 3, 8010 Graz, Austria
² Department of Physics, University of Helsinki, P.O. Box 64, 00014, Helsinki, Finland
³ Columbia Astrophysics Laboratory, Columbia University, 538 West 120th Street, New York, NY 10027, USA

^⋆ Corresponding author: daniel.milosic@uni-graz.at

Received: 20 November 2024
Accepted: 30 May 2025

Abstract

Context. Corotating interaction regions (CIRs) and their respective high-speed solar wind streams (HSSs) are one of the main drivers of geomagnetic storms. Studying the formation and evolution of CIRs is crucial for enhancing our understanding of the structuring of interplanetary space on a broad scale. Ultimately, this will lead to an improvement of solar wind models and forecasting of space weather conditions around Earth and other planets.

Aims. We aim to investigate the structure of CIRs in their early stages and explain their evolution throughout the inner heliosphere. We analyzed the radial and temporal evolution of the longitudinal extent of two distinct HSSs and the stream interaction regions (SIRs) they form in the inner heliosphere, associated with the “smiley coronal holes” on 26 October 2022.

Methods. We developed a scheme for the identification of different CIR regions. Applying that new method on Parker Solar Probe, Solar Orbiter, STEREO-A, and ACE in situ data, we identified three different regions of CIRs: perturbed slow wind, perturbed fast wind, and unperturbed fast wind. Measuring the longitudinal extent of these regions in a corotating reference frame, we exploited an advantageous spacecraft constellation to infer information about the radial and temporal evolution of the CIRs/SIRs. We compared the observed structures with three different solar wind modeling approaches.

Results. We identified two HSSs emanating from a source region close to two coronal holes. The first HSS, as observed at a radial distance of approximately 0.32 AU, formed a clear CIR with the surrounding slow wind. The second HSS, trailing behind the first HSS, has not formed an SIR before 0.35 AU, but has developed an SIR before 0.76 AU. The longitudinal extent of the individual structures, i.e., CIRs, SIRs and HSSs, changes over distance. The evolution of the CIR shows a very steep spiral curvature of up to 73±0.1 deg/AU. Comparisons to models showed that the apparent curvature of the CIR in the ecliptic plane is strongly underestimated.

Conclusions. Our current models cannot explain the observed behavior of the CIRs and HSSs in this study. The reasons might be a temporal evolution of the source coronal holes and the associated solar wind structures, an inaccurate modeling of the three-dimensional shape of the solar wind structures, or propagational effects such as deflections at the heliospheric current sheet. More analysis of multi-spacecraft in situ data is needed to gain information about the three-dimensional structure and temporal evolution of CIRs.