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.

High-resolution observations of flare precursors in the low solar atmosphere

Nature Astronomy volume 1, Article number: 0085 (2017) Cite this article

Subjects

Abstract

Solar flares are generally believed to be powered by free magnetic energy stored in the corona1, but the build up of coronal energy alone may be insufficient to trigger the flare to occur2. The flare onset mechanism is a critical but poorly understood problem, insights into which could be gained from small-scale energy releases known as precursors. These precursors are observed as small pre-flare brightenings in various wavelengths3–13 and also from certain small-scale magnetic configurations such as opposite-polarity fluxes14–16, where the magnetic orientation of small bipoles is opposite to that of the ambient main polarities. However, high-resolution observations of flare precursors together with the associated photospheric magnetic field dynamics are lacking. Here we study precursors of a flare using the unprecedented spatiotemporal resolution of the 1.6-m New Solar Telescope, complemented by new microwave data. Two episodes of precursor brightenings are initiated at a small-scale magnetic channel17–20 (a form of opposite-polarity flux) with multiple polarity inversions and enhanced magnetic fluxes and currents, lying near the footpoints of sheared magnetic loops. Microwave spectra corroborate that these precursor emissions originate in the atmosphere. These results provide evidence of low-atmospheric small-scale energy release, possibly linked to the onset of the main flare.

We study the 22 June 2015 M6.5 flare (SOL2015-06-22T18:23) using Hα (line-centre and red-wing) images and photospheric vector magnetograms obtained by the recently commissioned 1.6-m New Solar Telescope (NST)21,22 at Big Bear Solar Observatory (BBSO), which is stabilized by a high-order adaptive optics system (see Methods). In particular, the vector field data are taken by the Near InfraRed Imaging Spectropolarimeter (NIRIS)23 at the 1.56-μm Fe i line. These observations have the highest spatial resolution yet achieved for solar observations (~70 km for Hα and ~170 km for vector field) and rapid cadence (28 s for Hα and 87 s for vector field). Also used are flare microwave spectra and time profiles from the new Expanded Owens Valley Solar Array (EOVSA; see Methods), and time profiles of hard X-ray and soft X-ray fluxes from the Reuven Ramaty High Energy Solar Spectroscopic Imager24 and the Geostationary Operational Environmental Satellite-15, respectively. Ancillary data of full-disk corona images and magnetograms from the Solar Dynamics Observatory (SDO)25 are additionally used.

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

Prices vary by article type

from$1.95

to$39.95

Learn more

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

Figure 1: Precursor brightenings.
Figure 2: Magnetic field structure and evolution.
Figure 3: Properties of magnetic channel region.
Figure 4: Microwave emission.

References

  1. Priest, E. R. & Forbes, T. G. The magnetic nature of solar flares. Astron. Astrophys. Rev. 10, 313–377 (2002).

    Article  ADS  Google Scholar 

  2. Benz, A. O. Flare observations. Living Rev. Sol. Phys. 5, 1 (2008).

    Article  ADS  Google Scholar 

  3. Bumba, V. & Křivský, L. Chromospheric pre-flares. Bull. Astron. Inst. Czech 10, 221–223 (1959).

    ADS  Google Scholar 

  4. Martin, S. F. Preflare conditions, changes and events. Sol. Phys. 68, 217–236 (1980).

    Article  ADS  Google Scholar 

  5. van Hoven, G. & Hurford, G. J. Solar flare precursors. Adv. Space Res. 6, 83–91 (1986).

    Article  ADS  Google Scholar 

  6. Kai, K., Nakajima, H. & Kosugi, T. Radio observations of small activity prior to main energy release in solar flares. Publ. Astron. Soc. Jpn 35, 285–297 (1983).

    ADS  Google Scholar 

  7. Warren, H. P. & Warshall, A. D. Ultraviolet flare ribbon brightenings and the onset of hard X-ray emission. Astrophys. J. Lett. 560, L87–L90 (2001).

    Article  ADS  Google Scholar 

  8. Asai, A. et al. Preflare nonthermal emission observed in microwaves and hard X-rays. Publ. Astron. Soc. Jpn 58, L1–L5 (2006).

    Article  ADS  Google Scholar 

  9. Chifor, C., Tripathi, D., Mason, H. E. & Dennis, B. R. X-ray precursors to flares and filament eruptions. Astron. Astrophys. 472, 967–979 (2007).

    Article  ADS  Google Scholar 

  10. Battaglia, M., Fletcher, L. & Benz, A. O. Observations of conduction driven evaporation in the early rise phase of solar flares. Astron. Astrophys. 498, 891–900 (2009).

    Article  ADS  Google Scholar 

  11. Altyntsev, A. A., Fleishman, G. D., Lesovoi, S. V. & Meshalkina, N. S. Thermal to nonthermal energy partition at the early rise phase of solar flares. Astrophys. J. 758, 138 (2012).

    Article  ADS  Google Scholar 

  12. Fleishman, G. D., Nita, G. M. & Gary, D. E. Energy partitions and evolution in a purely thermal solar flare. Astrophys. J. 802, 122 (2015).

    Article  ADS  Google Scholar 

  13. Zhang, Y. et al. Solar radio bursts with spectral fine structures in preflares. Astrophys. J. 799, 30 (2015).

    Article  ADS  Google Scholar 

  14. Kusano, K. et al. Magnetic field structures triggering solar flares and coronal mass ejections. Astrophys. J. 760, 31 (2012).

    Article  ADS  Google Scholar 

  15. Toriumi, S. et al. The magnetic systems triggering the M6.6 class solar flare in NOAA active region 11158. Astrophys. J. 773, 128 (2013).

    Article  ADS  Google Scholar 

  16. Bamba, Y., Kusano, K., Yamamoto, T. T. & Okamoto, T. J. Study on the triggering process of solar flares based on Hinode/SOT observations. Astrophys. J. 778, 48 (2013).

    Article  ADS  Google Scholar 

  17. Zirin, H. & Wang, H. Narrow lanes of transverse magnetic field in sunspots. Nature 363, 426–428 (1993).

    Article  ADS  Google Scholar 

  18. Kubo, M. et al. Hinode observations of a vector magnetic field change associated with a flare on 2006 December 13. Publ. Astron. Soc. Jpn 59, S779–S784 (2007).

    Article  Google Scholar 

  19. Wang, H., Jing, J., Tan, C., Wiegelmann, T. & Kubo, M. Study of magnetic channel structure in active region 10930. Astrophys. J. 687, 658–667 (2008).

    Article  ADS  Google Scholar 

  20. Lim, E.-K., Chae, J., Jing, J., Wang, H. & Wiegelmann, T. The formation of a magnetic channel by the emergence of current-carrying magnetic fields. Astrophys. J. 719, 403–414 (2010).

    Article  ADS  Google Scholar 

  21. Goode, P. R., Coulter, R., Gorceix, N., Yurchyshyn, V. & Cao, W. The NST: first results and some lessons for ATST and EST. Astron. Nachr. 331, 620–623 (2010).

    Article  ADS  Google Scholar 

  22. Cao, W. et al. Scientific instrumentation for the 1.6 m New Solar Telescope in Big Bear. Astron. Nachr. 331, 636–639 (2010).

    Article  ADS  Google Scholar 

  23. Cao, W. et al. NIRIS: the second generation near-infrared imaging spectro-polarimeter for the 1.6 meter New Solar Telescope. Astron. Soc. Pacif. Conf. Series 463, 291–299 (2012).

    ADS  Google Scholar 

  24. Lin, R. P. et al. The Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI). Sol. Phys. 210, 3–32 (2002).

    Article  ADS  Google Scholar 

  25. Pesnell, W. D., Thompson, B. J. & Chamberlin, P. C. The Solar Dynamics Observatory (SDO). Sol. Phys. 275, 3–15 (2012).

    Article  ADS  Google Scholar 

  26. Kopp, R. A. & Pneuman, G. W. Magnetic reconnection in the corona and the loop prominence phenomenon. Sol. Phys. 50, 85–98 (1976).

    Article  ADS  Google Scholar 

  27. Janvier, M. et al. Electric currents in flare ribbons: observations and three-dimensional standard model. Astrophys. J. 788, 60 (2014).

    Article  ADS  Google Scholar 

  28. Fleishman, G. D., Nita, G. M., Kontar, E. P. & Gary, D. E. Narrowband gyrosynchrotron bursts: probing electron acceleration in solar flares. Astrophys. J. 826, 38 (2016).

    Article  ADS  Google Scholar 

  29. Stahli, M., Gary, D. E. & Hurford, G. J. High-resolution microwave spectra of solar bursts. Sol. Phys. 120, 351–368 (1989).

    Article  ADS  Google Scholar 

  30. Ahn, K., Cao, W., Shumko, S. & Chae, J. Data processing of the magnetograms for the Near InfraRed Imaging Spectropolarimeter at Big Bear Solar Observatory. Am. Astron. Soc. Sol. Phys. Div. Meeting 47, 2.07 (2016); https://ui.adsabs.harvard.edu/#abs/2016SPD....47.0207A/abstract

    Google Scholar 

  31. Tsuneta, S. et al. The Solar Optical Telescope for the Hinode mission: an overview. Sol. Phys. 249, 167–196 (2008).

    Article  ADS  Google Scholar 

  32. Schou, J. et al. Design and ground calibration of the Helioseismic and Magnetic Imager (HMI) instrument on the Solar Dynamics Observatory (SDO). Sol. Phys. 275, 229–259 (2012).

    Article  ADS  Google Scholar 

  33. Leka, K. D., Barnes, G. & Crouch, A. An automated ambiguity-resolution code for Hinode/SP vector magnetic field data. Astron. Soc. Pacif. Conf. Series 415, 365–368 (2009).

    ADS  Google Scholar 

  34. Metcalf, T. R. Resolving the 180-degree ambiguity in vector magnetic field measurements: the ‘minimum’ energy solution. Sol. Phys. 155, 235–242 (1994).

    Article  ADS  Google Scholar 

  35. Metcalf, T. R. et al. An overview of existing algorithms for resolving the 180° ambiguity in vector magnetic fields: quantitative tests with synthetic data. Sol. Phys. 237, 267–296 (2006).

    Article  ADS  Google Scholar 

  36. Gary, G. A. & Hagyard, M. J. Transformation of vector magnetograms and the problems associated with the effects of perspective and the azimuthal ambiguity. Sol. Phys. 126, 21–36 (1990).

    Article  ADS  Google Scholar 

  37. Wang, H., Ewell, M. W. Jr, Zirin, H. & Ai, G. Vector magnetic field changes associated with X-class flares. Astrophys. J. 424, 436–443 (1994).

    Article  ADS  Google Scholar 

  38. Wang, H. et al. The relationship between magnetic gradient and magnetic shear in five super active regions producing great flares. Chinese J. Astron. Astr. 6, 477–488 (2006).

    Article  ADS  Google Scholar 

  39. Metcalf, T. R. et al. Nonlinear force-free modeling of coronal magnetic fields. II. Modeling a filament arcade and simulated chromospheric and photospheric vector fields. Sol. Phys. 247, 269–299 (2008).

    Article  ADS  Google Scholar 

  40. Lemen, J. R. et al. The Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO). Sol. Phys. 275, 17–40 (2012).

    Article  ADS  Google Scholar 

  41. Gary, D. E. Early observations with the expanded Owens Valley Solar Array. Am. Astron. Soc. Sol. Phys. Div. Meeting 47, 301.01 (2016); https://ui.adsabs.harvard.edu/#abs/2016SPD....4730101G/abstract

    ADS  Google Scholar 

  42. Fleishman, G. D. & Kuznetsov, A. A. Fast gyrosynchrotron codes. Astrophys. J. 721, 1127–1141 (2010).

    Article  ADS  Google Scholar 

  43. Fleishman, G. D., Nita, G. M. & Gary, D. E. Dynamic magnetography of solar flaring loops. Astrophys. J. Lett. 698, L183–L187 (2009).

    Article  ADS  Google Scholar 

  44. Wiegelmann, T., Inhester, B. & Sakurai, T. Preprocessing of vector magnetograph data for a nonlinear force-free magnetic field reconstruction. Sol. Phys. 233, 215–232 (2006).

    Article  ADS  Google Scholar 

  45. Wheatland, M. S., Sturrock, P. A. & Roumeliotis, G. An optimization approach to reconstructing force-free fields. Astrophys. J. 540, 1150–1155 (2000).

    Article  ADS  Google Scholar 

  46. Wiegelmann, T. Optimization code with weighting function for the reconstruction of coronal magnetic fields. Sol. Phys. 219, 87–108 (2004).

    Article  ADS  Google Scholar 

  47. Liu, R. et al. Structure, stability, and evolution of magnetic flux ropes from the perspective of magnetic twist. Astrophys. J. 818, 148 (2016).

    Article  ADS  Google Scholar 

Download references

Acknowledgements

We thank the BBSO, EOVSA, SDO, RHESSI, GOES and Hinode teams for obtaining the data. This work was supported by NASA under grants NNX13AF76G, NNX13AG13G, NNX14AC12G, NNX14AC87G, NNX16AL67G and NNX16AF72G, and by the NSF under grants AGS 1250374, 1262772, 1250818, 1348513, 1408703 and 1539791. R.L. acknowledges support from the Thousand Young Talents Program of China and NSFC 41474151. K.K. acknowledges support from MEXT/JSPS KAKENHI 15H05814. The BBSO operation is supported by NJIT, US NSF AGS 1250818 and NASA NNX13AG14G grants, and partly supported by the Korea Astronomy and Space Science Institute and Seoul National University and by the Chinese Academy of Science’s strategic priority research programme, Grant No. XDB09000000.

Author information

Authors and Affiliations

  1. Space Weather Research Laboratory, New Jersey Institute of Technology, University Heights, Newark, 07102-1982, New Jersey, USA.

    Haimin Wang, Chang Liu, Yan Xu, Ju Jing, Na Deng & Nengyi Huang

  2. Big Bear Solar Observatory, New Jersey Institute of Technology, 40386 North Shore Lane, Big Bear City, 92314-9672, California, USA.

    Haimin Wang, Chang Liu, Kwangsu Ahn, Yan Xu, Ju Jing, Na Deng, Nengyi Huang & Wenda Cao

  3. Center for Solar-Terrestrial Research, New Jersey Institute of Technology, University Heights, Newark, 07102-1982, New Jersey, USA.

    Haimin Wang, Chang Liu, Yan Xu, Ju Jing, Na Deng, Nengyi Huang, Gregory D. Fleishman, Dale E. Gary & Wenda Cao

  4. Department of Geophysics and Planetary Sciences, CAS Key Laboratory of Geospace Environment, University of Science and Technology of China, Hefei, 230026, China.

    Rui Liu

  5. Collaborative Innovation Center of Astronautical Science and Technology, Hefei, China.

    Rui Liu

  6. Institute for Space-Earth Environmental Research, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8601, Japan.

    Kanya Kusano

Authors
  1. Haimin Wang
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Chang Liu
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Kwangsu Ahn
    View author publications

    You can also search for this author in PubMed Google Scholar

  4. Yan Xu
    View author publications

    You can also search for this author in PubMed Google Scholar

  5. Ju Jing
    View author publications

    You can also search for this author in PubMed Google Scholar

  6. Na Deng
    View author publications

    You can also search for this author in PubMed Google Scholar

  7. Nengyi Huang
    View author publications

    You can also search for this author in PubMed Google Scholar

  8. Rui Liu
    View author publications

    You can also search for this author in PubMed Google Scholar

  9. Kanya Kusano
    View author publications

    You can also search for this author in PubMed Google Scholar

  10. Gregory D. Fleishman
    View author publications

    You can also search for this author in PubMed Google Scholar

  11. Dale E. Gary
    View author publications

    You can also search for this author in PubMed Google Scholar

  12. Wenda Cao
    View author publications

    You can also search for this author in PubMed Google Scholar

Contributions

H.W. initiated the idea and carried out the data processing, analysis, interpretation and manuscript writing. C.L. contributed to the azimuth disambiguation of NIRIS data, data analysis and interpretation, and manuscript revision. K.A. developed tools for NIRIS data calibration, polarization inversion, and processed the NIRIS data. Y.X. was the Principal Investigator for this BBSO/NST observation run and contributed to the data processing. J.J. and N.D. contributed to the data analysis. N.H. contributed to this NST observation run. R.L. contributed to the NLFFF modelling and result interpretation. K.K. contributed to the interpretation of observations. G.D.F. and D.E.G. carried out the microwave data analysis and modelling. W.C. developed instruments at BBSO. All authors discussed the results and commented on the manuscript.

Corresponding authors

Correspondence to Haimin Wang or Wenda Cao.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary Information

Supplementary Figures 1–4 (PDF 1558 kb)

Supplementary Video 1

Time sequence of BBSO/NST H+ 0.6 Å images. (MP4 2131 kb)

Supplementary Video 2

Time sequence of BBSO/NST NIRIS photospheric vertical magnetic field images. (MP4 2160 kb)

Rights and permissions

Reprints and Permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Wang, H., Liu, C., Ahn, K. et al. High-resolution observations of flare precursors in the low solar atmosphere. Nat Astron 1, 0085 (2017). https://doi.org/10.1038/s41550-017-0085

Download citation

  • Received:

  • Accepted:

  • Published:

  • DOI: https://doi.org/10.1038/s41550-017-0085

This article is cited by

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