Highly structured slow solar wind emerging from an equatorial coronal hole

S D Bale; S T Badman; J W Bonnell; T A Bowen; D Burgess; A W Case; C A Cattell; B D G Chandran; C C Chaston; C H K Chen; J F Drake; T Dudok de Wit; J P Eastwood; R E Ergun; W M Farrell; C Fong; K Goetz; M Goldstein; K A Goodrich; P R Harvey; T S Horbury; G G Howes; J C Kasper; P J Kellogg; J A Klimchuk; K E Korreck; V V Krasnoselskikh; S Krucker; R Laker; D E Larson; R J MacDowall; M Maksimovic; D M Malaspina; J Martinez-Oliveros; D J McComas; N Meyer-Vernet; M Moncuquet; F S Mozer; T D Phan; M Pulupa; N E Raouafi; C Salem; D Stansby; M Stevens; A Szabo; M Velli; T Woolley; J R Wygant

doi:10.1038/s41586-019-1818-7

Highly structured slow solar wind emerging from an equatorial coronal hole

Nature. 2019 Dec;576(7786):237-242. doi: 10.1038/s41586-019-1818-7. Epub 2019 Dec 4.

Authors

S D Bale^{1

2

3

4}, S T Badman^{5

6}, J W Bonnell⁵, T A Bowen⁵, D Burgess⁷, A W Case⁸, C A Cattell⁹, B D G Chandran^{10

11}, C C Chaston⁵, C H K Chen⁷, J F Drake^{12

13

14}, T Dudok de Wit¹⁵, J P Eastwood¹⁶, R E Ergun¹⁷, W M Farrell¹⁸, C Fong^{5

6}, K Goetz⁹, M Goldstein^{19

20}, K A Goodrich⁵, P R Harvey⁵, T S Horbury¹⁶, G G Howes²¹, J C Kasper^{8

22}, P J Kellogg⁹, J A Klimchuk²³, K E Korreck⁸, V V Krasnoselskikh¹⁵, S Krucker^{5

24}, R Laker¹⁶, D E Larson⁵, R J MacDowall¹⁸, M Maksimovic²⁵, D M Malaspina¹⁷, J Martinez-Oliveros⁵, D J McComas²⁶, N Meyer-Vernet²⁵, M Moncuquet²⁵, F S Mozer⁵, T D Phan⁵, M Pulupa⁵, N E Raouafi²⁷, C Salem⁵, D Stansby¹⁶, M Stevens⁸, A Szabo²³, M Velli²⁸, T Woolley¹⁶, J R Wygant⁹

Affiliations

¹ Space Sciences Laboratory, University of California, Berkeley, CA, USA. bale@berkeley.edu.
² Physics Department, University of California, Berkeley, CA, USA. bale@berkeley.edu.
³ The Blackett Laboratory, Imperial College London, London, UK. bale@berkeley.edu.
⁴ School of Physics and Astronomy, Queen Mary University of London, London, UK. bale@berkeley.edu.
⁵ Space Sciences Laboratory, University of California, Berkeley, CA, USA.
⁶ Physics Department, University of California, Berkeley, CA, USA.
⁷ School of Physics and Astronomy, Queen Mary University of London, London, UK.
⁸ Smithsonian Astrophysical Observatory, Cambridge, MA, USA.
⁹ School of Physics and Astronomy, University of Minnesota, Minneapolis, MN, USA.
¹⁰ Department of Physics & Astronomy, University of New Hampshire, Durham, NH, USA.
¹¹ Space Science Center, University of New Hampshire, Durham, NH, USA.
¹² Department of Physics, University of Maryland, College Park, MD, USA.
¹³ Institute for Physical Science and Technology, University of Maryland, College Park, MD, USA.
¹⁴ Joint Space Science Institute, University of Maryland, College Park, MD, USA.
¹⁵ LPC2E, University of Orléans, CNRS, Orléans, France.
¹⁶ The Blackett Laboratory, Imperial College London, London, UK.
¹⁷ Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO, USA.
¹⁸ Code 695, NASA Goddard Space Flight Center, Greenbelt, MD, USA.
¹⁹ Goddard Planetary Heliophysics Institute, University of Maryland Baltimore County, Baltimore, MD, USA.
²⁰ Code 672, NASA Goddard Space Flight Center, Greenbelt, MD, USA.
²¹ Department of Physics and Astronomy, University of Iowa, Iowa City, IA, USA.
²² Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI, USA.
²³ Heliophysics Division, NASA Goddard Space Flight Center, Greenbelt, MD, USA.
²⁴ University of Applied Sciences and Arts Northwestern Switzerland, Windisch, Switzerland.
²⁵ LESIA, Observatoire de Paris, Université PSL, Sorbonne Université, CNRS, Meudon, France.
²⁶ Department of Astrophysical Sciences, Princeton University, Princeton, NJ, USA.
²⁷ Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA.
²⁸ Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, CA, USA.

PMID: 31802007
DOI: 10.1038/s41586-019-1818-7

Abstract

During the solar minimum, when the Sun is at its least active, the solar wind^1,2 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 streamers^5,6, from interchange reconnection near coronal hole boundaries^7,8, or within coronal holes with highly diverging magnetic fields^9,10. The heating mechanism required to drive the solar wind is also unresolved, although candidate mechanisms include Alfvén-wave turbulence^11,12, 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-instabilities^10,16 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.

Publication types

Research Support, U.S. Gov't, Non-P.H.S.
Research Support, Non-U.S. Gov't