Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Highly structured slow solar wind emerging from an equatorial coronal hole

Nature volume 576, pages 237–242 (2019)Cite this article

Subjects

Abstract

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.

This is a preview of subscription content, access via your institution

Relevant articles

Open Access articles citing this article.

Access options

Rent or buy this article

Get just this article for as long as you need it

$39.95

Learn more

Prices may be subject to local taxes which are calculated during checkout

Fig. 1: Radial magnetic field measurements are highly structured, map back to the Sun, and are consistent with a low source surface.
Fig. 2: Magnetic field reversals and plasma jets carry a Poynting flux.
Fig. 3: Plasma-wave activity near the perihelion differs in quiet wind and jets.
Fig. 4: Power spectral density and magnetic compressibility of magnetic field fluctuations in quiet and jet wind.

Data availability

The data used in this study are available at the NASA Space Physics Data Facility (SPDF), https://spdf.gsfc.nasa.gov/index.html.

References

  1. Parker, E. N. Dynamics of the interplanetary gas and magnetic fields. Astrophys. J. 128, 664–676 (1958).

    ADS  Google Scholar 

  2. Neugebauer, M. & Snyder, C. W. Solar plasma experiment. Science 138, 1095–1097 (1962).

    ADS  CAS  PubMed  Google Scholar 

  3. McComas, D. J. et al. Weaker solar wind from the polar coronal holes and the whole Sun. Geophys. Res. Lett. 35, L18103 (2008).

    ADS  Google Scholar 

  4. Abbo, L. et al. Slow solar wind: observations and modeling. Space Sci. Rev. 201, 55–108 (2016).

    ADS  Google Scholar 

  5. Lapenta, G. & Knoll, D. A. Effect of a converging flow at the streamer cusp on the genesis of the slow solar wind. Astrophys. J. 624, 1049–1056 (2005).

    ADS  Google Scholar 

  6. Einaudi, G., Boncinelli, P., Dahlburg, R. B. & Karpen, J. T. Formation of the slow solar wind in a coronal streamer. J. Geophys. Res. 104, 521–534 (1999).

    ADS  Google Scholar 

  7. Fisk, L. A. & Schwadron, N. A. The behavior of the open magnetic field of the Sun. Astrophys. J. 560, 425–438 (2001).

    ADS  Google Scholar 

  8. Antiochos, S. K., Mikic, Z., Titov, V. S., Lionello, R. & Linker, J. A. A model for the sources of the slow solar wind. Astrophys. J. 731, 112 (2011).

    ADS  Google Scholar 

  9. Wang, Y.-M. & Sheeley, N. R. On potential field models of the solar corona. Astrophys. J. 392, 310–319 (1992).

    ADS  CAS  Google Scholar 

  10. Cranmer, S. R. Coronal holes. Living Rev. Sol. Phys. 6, 3 (2009).

    ADS  PubMed  PubMed Central  Google Scholar 

  11. Hollweg, J. V. & Johnson, W. Transition region, corona, and solar wind in coronal holes: some two-fluid models. J. Geophys. Res. 93, 9547–9554 (1988).

    ADS  Google Scholar 

  12. Verdini, A., Velli, M., Matthaeus, W. H., Oughton, S. & Dmitruk, P. A turbulence-driven model for heating and acceleration of the fast wind in coronal holes. Astrophys. J. Lett. 708, 116–120 (2010).

    ADS  Google Scholar 

  13. Parker, E. N. Heating solar coronal holes. Astrophys. J. 372, 719–727 (1991).

    ADS  Google Scholar 

  14. Cranmer, S. R., Field, G. B. & Kohl, J. L. Spectroscopic constraints on models of ion cyclotron resonance heating in the polar solar corona and high-speed solar wind. Astrophys. J. 518, 937–947 (1999).

    ADS  CAS  Google Scholar 

  15. Fox, N. J. et al. The Solar Probe Plus mission: humanity’s first visit to our star. Space Sci. Rev. 204, 7–48 (2016).

    ADS  Google Scholar 

  16. Breneman, A. W. et al. STEREO and Wind observations of intense cyclotron harmonic waves at the Earth’s bow shock and inside the magnetosheath. J. Geophys. Res. Space Phys. 118, 7654–7664 (2013).

    ADS  Google Scholar 

  17. Bale, S. D. et al. The FIELDS instrument suite for Solar Probe Plus. Space Sci. Rev. 204, 49–82 (2016).

    ADS  CAS  PubMed  PubMed Central  Google Scholar 

  18. Parker, E. N. Dynamical theory of the solar wind. Space Sci. Rev. 4, 666–708 (1965).

    ADS  Google Scholar 

  19. Altschuler, M. D. & Newkirk, G. Magnetic fields and structure of the solar corona: 1. Methods of calculating coronal fields. Sol. Phys. 9, 131–149 (1969).

    Google Scholar 

  20. Schatten, K. H., Wilcox, J. M. & Ness, N. F. A model of interplanetary and coronal magnetic fields. Sol. Phys. 6, 442–455 (1969).

    ADS  Google Scholar 

  21. Arge, C. N. & Pizzo, V. J. Improvement in the prediction of solar wind conditions using near-real time solar magnetic field updates. J. Geophys. Res. Space Phys. 105, 10465–10479 (2000).

    ADS  Google Scholar 

  22. Riley, P. et al. A comparison between global solar magnetohydrodynamic and potential field source surface model results. Astrophys. J. 653, 1510–1516 (2006).

    ADS  Google Scholar 

  23. Hoeksema, J. T. Structure and Evolution of the Large Scale Solar and Heliospheric Magnetic Fields. PhD thesis, Stanford Univ. (1984).

  24. Lee, C. O. et al. Coronal field opens at lower height during the solar cycles 22 and 23 minimum periods: IMF comparison suggests the source surface should be lowered. Sol. Phys. 269, 367–388 (2011).

    ADS  CAS  Google Scholar 

  25. Riley, P. et al. Predicting the structure of the solar corona and inner heliosphere during Parker Solar Probe’s first perihelion pass. Astrophys. J. Lett. 874, 15 (2019).

    ADS  Google Scholar 

  26. Levine, R. H., Altschuler, M. D., Harvey, J. W. & Jackson, B. V. Open magnetic structures on the Sun. Astrophys. J. 215, 636–651 (1977).

    ADS  Google Scholar 

  27. Kasper, J. C. et al. Solar Wind Electrons Alphas and Protons (SWEAP) investigation. Space Sci. Rev. 204, 131 (2016).

    ADS  Google Scholar 

  28. McComas, D. J. et al. Probing the energetic particle environment near the Sun. Nature https://doi.org/10.1038/s41586-019-1811-1 (2019).

  29. Belcher, J. W. & Davis, L. Large-amplitude Alfvén waves in the interplanetary medium, 2. J. Geophys. Res. 76, 3534–3563 (1971).

    ADS  Google Scholar 

  30. Howes, G. G. et al. The slow mode nature of compressible wave power in solar wind turbulence. Astrophys. J. Lett. 753, 19 (2012).

    ADS  Google Scholar 

  31. Horbury, T. S. et al. Short, large-amplitude speed enhancements in the near-Sun fast solar wind. Mon. Not. R. Astron. Soc. 478, 1980–1986 (2018).

    ADS  Google Scholar 

  32. Gosling, J. T., Tian, H. & Phan, T. D. Pulsed Alfvén waves in the solar wind. Astrophys. J. Lett. 737, 35 (2011).

    ADS  Google Scholar 

  33. Balogh, A., Forsyth, R. J., Lucek, E. A., Horbury, T. S. & Smith, E. J. Heliospheric magnetic field polarity inversions at high heliographic latitudes. Geophys. Res. Lett. 26, 631–634 (1999).

    ADS  Google Scholar 

  34. Yamauchi, Y., Moore, R. L., Suess, S. T., Wang, H. & Sakurai, T. The magnetic structure of Hα macrospicules in solar coronal holes. Astrophys. J. 605, 511–520 (2004).

    ADS  Google Scholar 

  35. Raouafi, N.-E. & Stenborg, G. Role of transients in the sustainability of solar coronal plumes. Astrophys. J. 787, 118 (2014).

    ADS  Google Scholar 

  36. Roberts, M. A., Uritsky, V. M., DeVore, C. R. & Karpen, J. T. Simulated encounters of the Parker Solar Probe with a coronal-hole jet. Astrophys. J. 866, 14 (2018).

    ADS  Google Scholar 

  37. Meyer-Vernet, N., Issautier, K. & Moncuquet, M. Quasi-thermal noise spectroscopy: the art and the practice. J. Geophys. Res. Space Phys. 122, 7925–7945 (2017).

    ADS  Google Scholar 

  38. Schekochihin, A. A. et al. Astrophysical gyrokinetics: kinetic and fluid turbulent cascades in magnetized weakly collisional plasmas. Astrophys. J. 182, 310–377 (2009).

    Google Scholar 

  39. Matthaeus, W. H., Goldstein, M. L. & Smith, C. Evaluation of magnetic helicity in homogeneous turbulence. Phys. Rev. Lett. 48, 1256–1259 (1982).

    ADS  Google Scholar 

  40. Jian, L. K. et al. Electromagnetic waves near the proton cyclotron frequency: STEREO observations. Astrophys. J. 786, 123 (2014); erratum 847, 1 (2017).

    ADS  Google Scholar 

  41. Bruno, R. & Carbone, V. The solar wind as a turbulence laboratory. Living Rev. Sol. Phys. 10, 2 (2013).

    ADS  Google Scholar 

  42. Pulupa, M. et al. The Solar Probe Plus Radio Frequency Spectrometer: measurement requirements, analog design, and digital signal processing. J. Geophys. Res. Space Phys. 122, 2836–2854 (2017).

    ADS  Google Scholar 

  43. Malaspina, D. M. et al. The Digital Fields Board for the FIELDS instrument suite on the Solar Probe Plus mission: analog and digital signal processing. J. Geophys. Res. Space Phys. 121, 5088–5096 (2016).

    ADS  Google Scholar 

  44. Mozer, F. S. DC and low-frequency double probe electric field measurements in space. J. Geophys. Res. Space Phys. 121, 10942–10953 (2016).

    ADS  Google Scholar 

  45. Angelopoulos, V. et al. The Space Physics Environment Data Analysis System (SPEDAS). Space Sci. Rev. 215, 9 (2019).

    ADS  CAS  PubMed  PubMed Central  Google Scholar 

  46. Stansby, D. Dstansby/pfsspy: pfsspy 0.1.2 https://zenodo.org/record/3237053#.Xcqc-1f7SUk (2019).

  47. Yeates, A. Antyeates1983/pfss: first release of pfss code https://zenodo.org/record/1472183#.XcqdU1f7SUk (2018).

  48. Nolte, J. T. & Roelof, E. C. Large-scale structure of the interplanetary medium. I: High coronal source longitude of the quiet-time solar wind. Sol. Phys. 33, 241–257 (1973).

    ADS  Google Scholar 

  49. Neugebauer, M., et al. Spatial structure of the solar wind and comparisons with solar data and models. J. Geophys. Res. 103, 14587–14599 (1998).

    ADS  CAS  Google Scholar 

  50. Stansby, D., Horbury, T. S., Wallace, S. & Arge, C. N. Predicting large-scale coronal structure for Parker Solar Probe using open source software. RNAAS 3, 57 (2019).

    ADS  Google Scholar 

  51. Clark, R., Harvey, J., Hill, F. & Toner, C. GONG magnetogram zero-point-correction status. Bull. Am. Astron. Soc. 35, 822 (2003).

    ADS  Google Scholar 

  52. Hoeksema, J. T. et al. The Helioseismic and Magnetic Imager (HMI) vector magnetic field pipeline: overview and performance. Sol. Phys. 289, 3483–3530 (2014).

    ADS  Google Scholar 

  53. Schrijver, C. J. & DeRosa, M. L. Photospheric and heliospheric magnetic fields. Sol. Phys. 212, 165 (2003).

    ADS  Google Scholar 

Download references

Acknowledgements

The FIELDS experiment on the Parker Solar Probe spacecraft was designed and developed under NASA contract NNN06AA01C. The FIELDS team acknowledges the contributions of the Parker Solar Probe mission operations and spacecraft engineering teams at the Johns Hopkins University Applied Physics Laboratory. S.D.B. acknowledges the support of the Leverhulme Trust Visiting Professorship programme. Contributions from S.T.B. were supported by NASA Headquarters under the NASA Earth and Space Science Fellowship Program grant 80NSSC18K1201. This work uses data obtained by the Global Oscillation Network Group (GONG) programme, managed by the National Solar Observatory, which is operated by AURA, Inc. under a cooperative agreement with the National Science Foundation. The data were acquired by instruments operated by the Big Bear Solar Observatory, High Altitude Observatory, Learmonth Solar Observatory, Udaipur Solar Observatory, Instituto de Astrofísica de Canarias and Cerro Tololo Interamerican Observatory. D.B. was supported by UK STFC grant ST/P000622/1. J.P.E. and T.S.H. were supported by UK STFC grant ST/S000364/1. D.S. was supported by UK STFC grant ST/N000692/1. C.H.K.C. is supported by STFC Ernest Rutherford Fellowship number ST/N003748/2. T.D.d.W. and V.V.K. are supported by CNES.

Author information

Authors and Affiliations

  1. Space Sciences Laboratory, University of California, Berkeley, CA, USA

    S. D. Bale, S. T. Badman, J. W. Bonnell, T. A. Bowen, C. C. Chaston, C. Fong, K. A. Goodrich, P. R. Harvey, S. Krucker, D. E. Larson, J. Martinez-Oliveros, F. S. Mozer, T. D. Phan, M. Pulupa & C. Salem

  2. Physics Department, University of California, Berkeley, CA, USA

    S. D. Bale, S. T. Badman & C. Fong

  3. The Blackett Laboratory, Imperial College London, London, UK

    S. D. Bale, J. P. Eastwood, T. S. Horbury, R. Laker, D. Stansby & T. Woolley

  4. School of Physics and Astronomy, Queen Mary University of London, London, UK

    S. D. Bale, D. Burgess & C. H. K. Chen

  5. Smithsonian Astrophysical Observatory, Cambridge, MA, USA

    A. W. Case, J. C. Kasper, K. E. Korreck & M. Stevens

  6. School of Physics and Astronomy, University of Minnesota, Minneapolis, MN, USA

    C. A. Cattell, K. Goetz, P. J. Kellogg & J. R. Wygant

  7. Department of Physics & Astronomy, University of New Hampshire, Durham, NH, USA

    B. D. G. Chandran

  8. Space Science Center, University of New Hampshire, Durham, NH, USA

    B. D. G. Chandran

  9. Department of Physics, University of Maryland, College Park, MD, USA

    J. F. Drake

  10. Institute for Physical Science and Technology, University of Maryland, College Park, MD, USA

    J. F. Drake

  11. Joint Space Science Institute, University of Maryland, College Park, MD, USA

    J. F. Drake

  12. LPC2E, University of Orléans, CNRS, Orléans, France

    T. Dudok de Wit & V. V. Krasnoselskikh

  13. Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO, USA

    R. E. Ergun & D. M. Malaspina

  14. Code 695, NASA Goddard Space Flight Center, Greenbelt, MD, USA

    W. M. Farrell & R. J. MacDowall

  15. Goddard Planetary Heliophysics Institute, University of Maryland Baltimore County, Baltimore, MD, USA

    M. Goldstein

  16. Code 672, NASA Goddard Space Flight Center, Greenbelt, MD, USA

    M. Goldstein

  17. Department of Physics and Astronomy, University of Iowa, Iowa City, IA, USA

    G. G. Howes

  18. Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI, USA

    J. C. Kasper

  19. Heliophysics Division, NASA Goddard Space Flight Center, Greenbelt, MD, USA

    J. A. Klimchuk & A. Szabo

  20. University of Applied Sciences and Arts Northwestern Switzerland, Windisch, Switzerland

    S. Krucker

  21. LESIA, Observatoire de Paris, Université PSL, Sorbonne Université, CNRS, Meudon, France

    M. Maksimovic, N. Meyer-Vernet & M. Moncuquet

  22. Department of Astrophysical Sciences, Princeton University, Princeton, NJ, USA

    D. J. McComas

  23. Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA

    N. E. Raouafi

  24. Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, CA, USA

    M. Velli

Authors
  1. S. D. Bale
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. S. T. Badman
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. J. W. Bonnell
    View author publications

    You can also search for this author in PubMed Google Scholar

  4. T. A. Bowen
    View author publications

    You can also search for this author in PubMed Google Scholar

  5. D. Burgess
    View author publications

    You can also search for this author in PubMed Google Scholar

  6. A. W. Case
    View author publications

    You can also search for this author in PubMed Google Scholar

  7. C. A. Cattell
    View author publications

    You can also search for this author in PubMed Google Scholar

  8. B. D. G. Chandran
    View author publications

    You can also search for this author in PubMed Google Scholar

  9. C. C. Chaston
    View author publications

    You can also search for this author in PubMed Google Scholar

  10. C. H. K. Chen
    View author publications

    You can also search for this author in PubMed Google Scholar

  11. J. F. Drake
    View author publications

    You can also search for this author in PubMed Google Scholar

  12. T. Dudok de Wit
    View author publications

    You can also search for this author in PubMed Google Scholar

  13. J. P. Eastwood
    View author publications

    You can also search for this author in PubMed Google Scholar

  14. R. E. Ergun
    View author publications

    You can also search for this author in PubMed Google Scholar

  15. W. M. Farrell
    View author publications

    You can also search for this author in PubMed Google Scholar

  16. C. Fong
    View author publications

    You can also search for this author in PubMed Google Scholar

  17. K. Goetz
    View author publications

    You can also search for this author in PubMed Google Scholar

  18. M. Goldstein
    View author publications

    You can also search for this author in PubMed Google Scholar

  19. K. A. Goodrich
    View author publications

    You can also search for this author in PubMed Google Scholar

  20. P. R. Harvey
    View author publications

    You can also search for this author in PubMed Google Scholar

  21. T. S. Horbury
    View author publications

    You can also search for this author in PubMed Google Scholar

  22. G. G. Howes
    View author publications

    You can also search for this author in PubMed Google Scholar

  23. J. C. Kasper
    View author publications

    You can also search for this author in PubMed Google Scholar

  24. P. J. Kellogg
    View author publications

    You can also search for this author in PubMed Google Scholar

  25. J. A. Klimchuk
    View author publications

    You can also search for this author in PubMed Google Scholar

  26. K. E. Korreck
    View author publications

    You can also search for this author in PubMed Google Scholar

  27. V. V. Krasnoselskikh
    View author publications

    You can also search for this author in PubMed Google Scholar

  28. S. Krucker
    View author publications

    You can also search for this author in PubMed Google Scholar

  29. R. Laker
    View author publications

    You can also search for this author in PubMed Google Scholar

  30. D. E. Larson
    View author publications

    You can also search for this author in PubMed Google Scholar

  31. R. J. MacDowall
    View author publications

    You can also search for this author in PubMed Google Scholar

  32. M. Maksimovic
    View author publications

    You can also search for this author in PubMed Google Scholar

  33. D. M. Malaspina
    View author publications

    You can also search for this author in PubMed Google Scholar

  34. J. Martinez-Oliveros
    View author publications

    You can also search for this author in PubMed Google Scholar

  35. D. J. McComas
    View author publications

    You can also search for this author in PubMed Google Scholar

  36. N. Meyer-Vernet
    View author publications

    You can also search for this author in PubMed Google Scholar

  37. M. Moncuquet
    View author publications

    You can also search for this author in PubMed Google Scholar

  38. F. S. Mozer
    View author publications

    You can also search for this author in PubMed Google Scholar

  39. T. D. Phan
    View author publications

    You can also search for this author in PubMed Google Scholar

  40. M. Pulupa
    View author publications

    You can also search for this author in PubMed Google Scholar

  41. N. E. Raouafi
    View author publications

    You can also search for this author in PubMed Google Scholar

  42. C. Salem
    View author publications

    You can also search for this author in PubMed Google Scholar

  43. D. Stansby
    View author publications

    You can also search for this author in PubMed Google Scholar

  44. M. Stevens
    View author publications

    You can also search for this author in PubMed Google Scholar

  45. A. Szabo
    View author publications

    You can also search for this author in PubMed Google Scholar

  46. M. Velli
    View author publications

    You can also search for this author in PubMed Google Scholar

  47. T. Woolley
    View author publications

    You can also search for this author in PubMed Google Scholar

  48. J. R. Wygant
    View author publications

    You can also search for this author in PubMed Google Scholar

Contributions

S.D.B. wrote the manuscript with substantial contributions from S.T.B., B.D.G.C., C.H.K.C., T.S.H., M. Maksimovic, T.D.P. and M.V. All authors participated in the data interpretation, and read and commented upon the manuscript. S.D.B. led the FIELDS instrument team with contributions from J.W.B., T.A.B, T.D.d.W., K.G., P.R.H., D.E.L., R.J.M., M. Maksimovic, D.M.M., M.P. and N.E.R.

Corresponding author

Correspondence to S. D. Bale.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Extended data figures and tables

Extended Data Fig. 1 Variation of PFSS neutral line topology with time and magnetogram choice at RSS = 2.5R⊙.

Colour maps of BR at the source surface from PFSS extractions with source-surface radius RSS = 2.5R⊙. Red indicates positive polarity and blue indicates negative polarity. The black line shows the PIL (the contour of BR = 0). Superposed is the ballistically projected PSP trajectory coloured by the measured polarity. Perihelion occurred around 330° longitude. Left to right, the columns show extractions from the NSO/GONG, SDO/HMI and DeRosa LMSAL models. From top to bottom, the models are evaluated at a weekly cadence spanning six weeks about perihelion, with input magnetograms from each source taken as close in time as possible. The grey shading shows the region ±60° about the central meridian on the date of the model evaluation, indicating the portion of the Sun that could be observed at the time of observation.

Extended Data Fig. 2 Variation of PFSS neutral line topology with time and magnetogram choice at RSS = 2.0R⊙.

Colour maps of BR at the source surface from PFSS extractions with RSS = 2.0R⊙. Other features are as described in Extended Data Fig. 1.

Extended Data Fig. 3 Variation of PFSS Neutral Line topology with time and magnetogram choice at RSS = 1.2R⊙.

Colour maps of BR at the source surface from PFSS extractions with RSS = 1.2R⊙. Other features are as described in Extended Data Fig. 1.

Extended Data Fig. 4 Synoptic maps of extreme-ultraviolet coronal emission from Carrington rotation 2,210, assembled from the STEREO-A/EUVI and SDO/AIA instruments.

Top, 171-Å data showing coronal Fe ix emission at around 600,000 K. This is the background of Fig. 1c, d. Bottom, 193-Å (AIA) and 195-Å (EUVI) data showing emission from coronal Fe xii emission at around 1,000,000 K. The brightness is positively correlated with the integrated plasma density squared along the line of sight. The dark regions in both images are probable locations of coronal holes, which are threaded by open magnetic field lines that allow plasma to evacuate into interplanetary space, resulting in under-dense regions. Carrington rotation 2,210 occurred from 20:51 26 October 2018 ut to 04:11 23 November 2018 ut.

Extended Data Fig. 5 During encounter 1, PSP connected magnetically to a small negative-polarity equatorial coronal hole.

This schematic shows a potential field extrapolation of the solar magnetic field at the time of the first perihelion pass of PSP. The solar surface is shown, coloured by AIA 211-Å extreme-ultraviolet emission (see Extended Data Fig. 4 for other wavelengths). Coronal holes appear as a lighter shade. Superposed are various field lines initialized at the solar disk. Black lines indicate closed loops, blue and red illustrate open field lines with negative and positive polarities, respectively. As depicted here and in Fig. 1c, d, at perihelion PSP connected to a negative equatorial coronal hole. The ‘switchbacks’ (the jets) observed by PSP (Fig. 1a) are illustrated as kinks in the open field lines emerging from the coronal hole that connect to PSP. (Note that neither the radial distance to the spacecraft nor the scale or amplitude of the jets or switchbacks are to scale.) Spacecraft graphic is courtesy of NASA/Johns Hopkins APL.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Bale, S.D., Badman, S.T., Bonnell, J.W. et al. Highly structured slow solar wind emerging from an equatorial coronal hole. Nature 576, 237–242 (2019). https://doi.org/10.1038/s41586-019-1818-7

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/s41586-019-1818-7

This article is cited by

Comments

By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.

Search

Advanced search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing