Letter to the Editor

First polar observations of the fast solar wind with the Metis – Solar Orbiter coronagraph: Role of 2D turbulence energy dissipation in the wind acceleration

¹ National Institute for Astrophysics, Astrophysical Observatory of Torino, Via Osservatorio 20, 10025 Pino Torinese, Italy
e-mail: daniele.telloni@inaf.it
² Center for Space Plasma and Aeronomic Research, University of Alabama in Huntsville, Huntsville, AL 35805, USA
³ Department of Space Science, University of Alabama in Huntsville, Huntsville, AL 35805, USA
⁴ National Institute for Astrophysics, Astronomical Observatory of Capodimonte, Salita Moiariello 16, 80131 Napoli, Italy
⁵ National Institute for Astrophysics, Astrophysical Observatory of Arcetri, Largo Enrico Fermi 5, 50125 Firenze, Italy
⁶ National Institute for Astrophysics, Astrophysical Observatory of Catania, Via Santa Sofia 78, 95123 Catania, Italy
⁷ University of Catania, Department of Physics and Astronomy, Via Santa Sofia 64, 95123 Catania, Italy
⁸ National Research Council, Institute for Photonics and Nanotechnologies, Via Trasea 7, 35131 Padova, Italy
⁹ Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
¹⁰ University of Urbino Carlo Bo, Department of Pure and Applied Sciences, Via Santa Chiara 27, 61029 Urbino, Italy
¹¹ National Institute for Nuclear Physics, Section in Florence, Via Bruno Rossi 1, 50019 Sesto Fiorentino, Italy
¹² Czech Academy of Sciences, Astronomical Institute, Fričova 298, 25165 Ondřejov, Czech Republic
¹³ University of Wrocław, Centre of Scientific Excellence – Solar and Stellar Activity, ul. Kopernika 11, 51-622 Wrocław, Poland
¹⁴ National Institute for Astrophysics, Astronomical Observatory of Trieste, Località Basovizza 302, 34149 Trieste, Italy
¹⁵ Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
¹⁶ National Aeronautics and Space Administration, Headquarters, Washington, DC 20546, USA
¹⁷ University of Padua, Department of Physics and Astronomy, Via Francesco Marzolo 8, 35131 Padova, Italy
¹⁸ University of Florence, Department of Physics and Astronomy, Via Giovanni Sansone 1, 50019 Sesto Fiorentino, Italy
¹⁹ Italian Space Agency, Via del Politecnico snc, 00133 Roma, Italy
²⁰ National Institute for Astrophysics, Institute of Space Astrophysics and Cosmic Physics of Milan, Via Alfonso Corti 12, 20133 Milano, Italy
²¹ National Research Council, Institute for the Science and Technology of Plasmas, Via Amendola 122/D, 70126 Bari, Italy
²² Swedish Institute of Space Physics, Ångström Laboratory, Lägerhyddsvägen 1, 751 21 Uppsala, Sweden
²³ Université de Lyon, Centre National de la Recherche Scientifique, École Centrale de Lyon, Institut National des Sciences Appliquées de Lyon, Université Claude Bernard Lyon 1, Laboratoire de Mécanique des Fluides et d’Acoustique, 69134 Écully, France
²⁴ National Institute for Astrophysics, Institute for Space Astrophysics and Planetology, Via del Fosso del Cavaliere 100, 00133 Roma, Italy

Received: 21 December 2022
Accepted: 27 January 2023

Abstract

Context. The fast solar wind is known to emanate from polar coronal holes.

Aims. This Letter reports the first estimate of the expansion rate of polar coronal flows performed by the Metis coronagraph on board Solar Orbiter.

Methods. By exploiting simultaneous measurements in polarized white light and ultraviolet intensity of the neutral hydrogen Lyman-α line, it was possible to extend observations of the outflow velocity of the main component of the solar wind from polar coronal holes out to 5.5 R_⊙, the limit of diagnostic applicability and observational capabilities.

Results. We complement the results obtained with analogous polar observations performed with the UltraViolet Coronagraph Spectrometer on board the SOlar and Heliospheric Observatory during the previous full solar activity cycle, and find them to be satisfactorily reproduced by a magnetohydrodynamic turbulence model.

Conclusions. This suggests that the dissipation of 2D turbulence energy is a viable mechanism for coronal plasma heating and the subsequent acceleration of the fast solar wind.