Alfvénic solar wind intervals observed by Solar Orbiter: Exploiting the capability of the SWA plasma suite and source region investigation
Year: 2026
Type: article
Abstract: Context. Fast and slow solar wind have distinct properties linked to their solar sources. The Alfvénic slow wind complicates the usual classification by solar-wind speed, especially at intermediate speeds. The Solar Wind Analyzer (SWA) on Solar Orbiter offers unique capabilities to investigate how Alfvénic slow wind differs from classical fast wind, and relates these differences to their solar origins. Aims. In September 2022, Solar Orbiter moved inbound toward the Sun from 0.59 to 0.38 AU, and observed several Alfvénic streams: one fast wind (F), three Alfvénic slow wind intervals (AS1, AS2, AS3), and a moderate fast wind (MF); a non-Alfvénic slow wind (S) interval was included for comparison. We analyzed these streams to highlight their similarities and differences. Methods. We combined plasma parameters from all SWA sensors with magnetic field measurements from the magnetometer (MAG). A spectral analysis of magnetic and velocity fluctuations was used to characterize the Alfvénicity. The magnetic connectivity of each stream to its solar source was examined using potential field source surface extrapolation combined with ballistic backmapping from the spacecraft. Results. Proton velocity distribution functions exhibit anisotropies and field-aligned beams typical of Alfvénic streams, while electron strahl populations become progressively broader and weaker from fast to non-Alfvénic slow wind. Heavy-ion composition shows a similarly ordered transition, where the Alfvénic slow wind displays intermediate charge-state ratios between fast and non-Alfvénic slow wind. Magnetic connectivity analysis associates the fast wind with a large coronal hole, whereas the Alfvénic slow wind intervals connect to open-field regions near pseudostreamers and overexpanded coronal-hole boundaries. Spectral analysis indicates that most Alfvénic streams remain close to energy equipartition despite their different heliocentric distances and bulk speeds. Altogether, these results support the interpretation of Alfvénic slow wind as the low-speed extension of coronal-hole-associated Alfvénic plasma undergoing a distinct acceleration and transport history. Conclusions. The combined SWA observations offer key insights into how turbulence, particle transport, and coronal source conditions jointly shape the evolution of Alfvénic solar wind streams, revealing a coherent transition between fast, Alfvénic slow, and non-Alfvénic slow wind regimes.
Source: Astronomy and Astrophysics
Authors: R. D’Amicis, J. M. Raines, S. Benella, O. Panasenco, M. Velli, G. Nicolaou, C. J. Owen, R. M. Dewey, P. Louarn, A. Fedorov, S. T. Lepri, B. L. Alterman, D. Perrone, R. De Marco, R. Bruno, L. Sorriso-Valvo, O. S. Dhamane, Y. Rivera, O. R. Kieokaew, D. Verscharen, G. Consolini, S. Yardley, V. Réville, D. Telloni, D. Baker, G. Lewis, G. Watson, C. Anekallu, K. Darwish, L. Prech, S. Livi, T. Horbury, G. Mele, V. Fortunato, F. Monti
Institutions: Institute for Space Astrophysics and Planetology, National Institute for Astrophysics, University of Michigan, Advanced Heliophysics, University College London, Centre National de la Recherche Scientifique, Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse, Goddard Space Flight Center, Heliophysics Science Division, Agenzia Spaziale Italiana, Institute for the Science and Technology of Plasmas, National Research Council, KTH Royal Institute of Technology, Center for Astrophysics Harvard & Smithsonian, Northumbria University, Osservatorio Astrofisico di Torino, Charles University, Southwest Research Institute, Imperial College London, Planetek Italia
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,865
OpenAlex ID: W7172012010