Interchange reconnection as the source of the fast solar wind within coronal holes

S D Bale; J F Drake; M D McManus; M I Desai; S T Badman; D E Larson; M Swisdak; T S Horbury; N E Raouafi; T Phan; M Velli; D J McComas; C M S Cohen; D Mitchell; O Panasenco; J C Kasper

doi:10.1038/s41586-023-05955-3

Interchange reconnection as the source of the fast solar wind within coronal holes

Nature. 2023 Jun;618(7964):252-256. doi: 10.1038/s41586-023-05955-3. Epub 2023 Jun 7.

Authors

S D Bale^{1

2}, J F Drake^{3

4}, M D McManus^{5

6}, M I Desai⁷, S T Badman⁸, D E Larson⁶, M Swisdak⁴, T S Horbury⁹, N E Raouafi¹⁰, T Phan⁶, M Velli^{11

12}, D J McComas¹³, C M S Cohen¹⁴, D Mitchell¹⁰, O Panasenco¹⁵, J C Kasper^{16

17}

Affiliations

¹ Physics Department, University of California, Berkeley, CA, USA. bale@berkeley.edu.
² Space Sciences Laboratory, University of California, Berkeley, CA, USA. bale@berkeley.edu.
³ Department of Physics, the Institute for Physical Science and Technology and the Joint Space Institute, University of Maryland, College Park, MD, USA.
⁴ Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, MD, USA.
⁵ Physics Department, University of California, Berkeley, CA, USA.
⁶ Space Sciences Laboratory, University of California, Berkeley, CA, USA.
⁷ Southwest Research Institute, San Antonio, TX, USA.
⁸ Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA.
⁹ The Blackett Laboratory, Imperial College London, London, UK.
¹⁰ Johns Hopkins Applied Physics Laboratory, Laurel, MD, USA.
¹¹ Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, CA, USA.
¹² International Space Science Institute, Bern, Switzerland.
¹³ Department of Astrophysical Sciences, Princeton University, Princeton, NJ, USA.
¹⁴ California Institute of Technology, Pasadena, CA, USA.
¹⁵ Advanced Heliophysics Inc., Los Angeles, CA, USA.
¹⁶ BWX Technologies, Inc., Washington, DC, USA.
¹⁷ Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI, USA.

Abstract

The fast solar wind that fills the heliosphere originates from deep within regions of open magnetic field on the Sun called 'coronal holes'. The energy source responsible for accelerating the plasma is widely debated; however, there is evidence that it is ultimately magnetic in nature, with candidate mechanisms including wave heating^1,2 and interchange reconnection^3-5. The coronal magnetic field near the solar surface is structured on scales associated with 'supergranulation' convection cells, whereby descending flows create intense fields. The energy density in these 'network' magnetic field bundles is a candidate energy source for the wind. Here we report measurements of fast solar wind streams from the Parker Solar Probe (PSP) spacecraft⁶ that provide strong evidence for the interchange reconnection mechanism. We show that the supergranulation structure at the coronal base remains imprinted in the near-Sun solar wind, resulting in asymmetric patches of magnetic 'switchbacks'^7,8 and bursty wind streams with power-law-like energetic ion spectra to beyond 100 keV. Computer simulations of interchange reconnection support key features of the observations, including the ion spectra. Important characteristics of interchange reconnection in the low corona are inferred from the data, including that the reconnection is collisionless and that the energy release rate is sufficient to power the fast wind. In this scenario, magnetic reconnection is continuous and the wind is driven by both the resulting plasma pressure and the radial Alfvénic flow bursts.