| Issue |
A&A
Volume 677, September 2023
|
|
|---|---|---|
| Article Number | A108 | |
| Number of page(s) | 22 | |
| Section | The Sun and the Heliosphere | |
| DOI | https://doi.org/10.1051/0004-6361/202347146 | |
| Published online | 12 September 2023 | |
Variability of the slow solar wind: New insights from modelling and PSP-WISPR observations⋆
1
Rosseland Centre for Solar Physics, University of Oslo, Postboks 1029, Blindern, 0315 Oslo, Norway
e-mail: nicolas.poirier@astro.uio.no
2
Institute of Theoretical Astrophysics, University of Oslo, Postboks 1029, Blindern, 0315 Oslo, Norway
3
IRAP, Université Toulouse III – Paul Sabatier, CNRS, CNES, Toulouse, France
4
The Johns Hopkins University Applied Physics Laboratory, 11101 Johns Hopkins Road, Laurel, MD 20723, USA
Received:
9
June
2023
Accepted:
11
July
2023
Aims. We analyse the signature and origin of transient structures embedded in the slow solar wind, and observed by the Wide-Field Imager for Parker Solar Probe (WISPR) during its first ten passages close to the Sun. WISPR provides a new in-depth vision on these structures, which have long been speculated to be a remnant of the pinch-off magnetic reconnection occurring at the tip of helmet streamers.
Methods. We pursued the previous modelling works of Réville et al. (2020, ApJ, 895, L20; 2022, A&A, 659, A110) that simulate the dynamic release of quasi-periodic density structures into the slow wind through a tearing-induced magnetic reconnection at the tip of helmet streamers. Synthetic WISPR white-light (WL) images are produced using a newly developed advanced forward modelling algorithm that includes an adaptive grid refinement to resolve the smallest transient structures in the simulations. We analysed the aspect and properties of the simulated WL signatures in several case studies that are typical of solar minimum and near-maximum configurations.
Results. Quasi-periodic density structures associated with small-scale magnetic flux ropes are formed by tearing-induced magnetic reconnection at the heliospheric current sheet and within 3 − 7 R⊙. Their appearance in WL images is greatly affected by the shape of the streamer belt and the presence of pseudo-streamers. The simulations show periodicities on ≃90 − 180 min, ≃7 − 10 h, and ≃25 − 50 h timescales, which are compatible with WISPR and past observations.
Conclusions. This work shows strong evidence for a tearing-induced magnetic reconnection contributing to the long-observed high variability of the slow solar wind.
Key words: solar wind / methods: numerical / methods: observational / magnetohydrodynamics (MHD) / instabilities / magnetic reconnection
Movies (Figs. 6–9, 11, B.1–B.3) are available at https://www.aanda.org.
© The Authors 2023
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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