• DOI:10.1038/s41586-019-1818-7
• Corpus ID: 208623434

Highly structured slow solar wind emerging from an equatorial coronal hole

@article{Bale2019HighlySS,
  title={Highly structured slow solar wind emerging from an equatorial coronal hole},
  author={Stuart. D. Bale and Samuel T. Badman and J. W. Bonnell and Trevor A. Bowen and David Burgess and Anthony William Case and Cynthia A. Cattell and Benjamin D. G. Chandran and Christopher C. Chaston and C. H. K. Chen and James F. Drake and Thierry Dudok de Wit and Jonathan P. Eastwood and Robert E. Ergun and William M. Farrell and C. Fong and Keith Goetz and Melvyn L. Goldstein and Katherine Amanda Goodrich and Peter R. Harvey and Timothy S. Horbury and Gregory Gershom Howes and Justin C. Kasper and Paul J. Kellogg and James A. Klimchuk and Kelly E. Korreck and Vladimir Krasnoselskikh and S{\"a}m Krucker and Ronan Laker and Davin E. Larson and Robert J. Macdowall and Milan Maksimovi{\'c} and David M. Malaspina and Juan Carlos Mart{\'i}nez-Oliveros and D. J. Mccomas and Nicole Meyer‐Vernet and Michel Moncuquet and Forrest S. Mozer and Tai D. Phan and Marc P. Pulupa and Noureddine Raouafi and Chadi S. Salem and David Stansby and Michael Louis Stevens and Adam Szabo and Marco Velli and Thomas Woolley and John R. Wygant},
  journal={Nature},
  year={2019},
  pages={1-6}
}

• S. Bale, S. Badman, +45 authors J. Wygant
• Published 1 December 2019
• Physics
• Nature

During the solar minimum, when the Sun is at its least active, the solar wind1,2 is observed at high latitudes as a predominantly fast (more than 500 kilometres per second), highly Alfvénic rarefied stream of plasma originating from deep within coronal holes. Closer to the ecliptic plane, the solar wind is interspersed with a more variable slow wind3 of less than 500 kilometres per second. The precise origins of the slow wind streams are less certain4; theories and observations suggest that they may originate at the tips of helmet streamers5,6, from interchange reconnection near coronal hole boundaries7,8, or within coronal holes with highly diverging magnetic fields9,10. The heating mechanism required to drive the solar wind is also unresolved, although candidate mechanisms include Alfvén-wave turbulence11,12, heating by reconnection in nanoflares13, ion cyclotron wave heating14 and acceleration by thermal gradients1. At a distance of one astronomical unit, the wind is mixed and evolved, and therefore much of the diagnostic structure of these sources and processes has been lost. Here we present observations from the Parker Solar Probe15 at 36 to 54 solar radii that show evidence of slow Alfvénic solar wind emerging from a small equatorial coronal hole. The measured magnetic field exhibits patches of large, intermittent reversals that are associated with jets of plasma and enhanced Poynting flux and that are interspersed in a smoother and less turbulent flow with a near-radial magnetic field. Furthermore, plasma-wave measurements suggest the existence of electron and ion velocity-space micro-instabilities10,16 that are associated with plasma heating and thermalization processes. Our measurements suggest that there is an impulsive mechanism associated with solar-wind energization and that micro-instabilities play a part in heating, and we provide evidence that low-latitude coronal holes are a key source of the slow solar wind.Measurements from the Parker Solar Probe show that slow solar wind near the Sun’s equator originates in coronal holes.