Needle-like structures discovered on positively charged lightning branches

Abstract

Lightning is a dangerous yet poorly understood natural phenomenon. Lightning forms a network of plasma channels propagating away from the initiation point with both positively and negatively charged ends—called positive and negative leaders1. Negative leaders propagate in discrete steps, emitting copious radio pulses in the 30–300-megahertz frequency band2,3,4,5,6,7,8 that can be remotely sensed and imaged with high spatial and temporal resolution9,10,11. Positive leaders propagate more continuously and thus emit very little high-frequency radiation12. Radio emission from positive leaders has nevertheless been mapped13,14,15, and exhibits a pattern that is different from that of negative leaders11,12,13,16,17. Furthermore, it has been inferred that positive leaders can become transiently disconnected from negative leaders9,12,16,18,19,20, which may lead to current pulses that both reconnect positive leaders to negative leaders11,16,17,20,21,22 and cause multiple cloud-to-ground lightning events1. The disconnection process is thought to be due to negative differential resistance18, but this does not explain why the disconnections form primarily on positive leaders22, or why the current in cloud-to-ground lightning never goes to zero23. Indeed, it is still not understood how positive leaders emit radio-frequency radiation or why they behave differently from negative leaders. Here we report three-dimensional radio interferometric observations of lightning over the Netherlands with unprecedented spatiotemporal resolution. We find small plasma structures—which we call ‘needles’—that are the dominant source of radio emission from the positive leaders. These structures appear to drain charge from the leader, and are probably the reason why positive leaders disconnect from negative ones, and why cloud-to-ground lightning connects to the ground multiple times.

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Fig. 1: Map of the 2017 flash.
Fig. 2: Expanded sections of Fig. 1, with a positive leader on the left and a negative leader on the right.
Fig. 3: A region around the structure labelled N4 in Fig. 2.
Fig. 4: A portion of a positive leader, in light of the behaviour of needles.

Data availability

To obtain the data, readers should submit a support request to the radio observatory via the ASTRON website (http://www.astron.nl). The 2016 flash was from project LC6_003, observation L526419, time stamp D20160712T173455.100Z. The 2017 flash was from LC8 commissioning data, observation L612746, time stamp D20170929T202255.000Z.

Code availability

The data was processed with software archived at https://github.com/Bhare8972/LOFAR-LIM, version 2018.11.8.

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Acknowledgements

The LOFAR cosmic ray key science project acknowledges funding from an Advanced Grant of the European Research Council (FP/2007–2013)/ERC Grant Agreement number 227610. The project has also received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement number 640130). We furthermore acknowledge financial support from FOM (FOM-project 12PR304). A.N. is supported by the DFG (research fellowship NE 2031/2-1). T.W. is supported by the DFG (research fellowship NE WI 4946/1-1). This paper is based (in part) on data obtained with the International LOFAR Telescope (ILT) under project code LC6_003. LOFAR25 is the Low Frequency Array designed and constructed by ASTRON. It has observing, data processing and data storage facilities in several countries, that are owned by various parties (each with their own funding sources), and that are collectively operated by the ILT foundation under a joint scientific policy. The ILT resources have benefited from the following recent major funding sources: CNRS-INSU, Observatoire de Paris and Université d’Orléans, France; BMBF, MIWF-NRW, MPG, Germany; Science Foundation Ireland (SFI), Department of Business, Enterprise and Innovation (DBEI), Ireland; NWO, The Netherlands; The Science and Technology Facilities Council, UK; Ministry of Science and Higher Education, Poland.

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Nature thanks E. Williams and the other anonymous reviewer(s) for their contribution to the peer review of this work.

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Contributions

B.M.H. and O.S. wrote the manuscript, developed the imaging technique and analysed the results. T.N.G.T., S.B., S.t.V., A.B., A.C., H.F., J.R.H., T.H., P.M., K.M., A.N., J.P.R., L.R., P.S. and T.W. are members of the LOFAR cosmic-ray key science project, and contributed to the acquisition, calibration and analysis of the LOFAR data. J.A., I.M.A., M.J.B., R.B., J.W.B., W.N.B., M.B., H.R.B., B.C., R.A.F., E.d.G., S.D., J.E., M.A.G., J.M.G., A.W.G., M.P.v.H., J.W.T.H., M.H., A.J.v.d.H., M.I., L.V.E.K., A.K., P.M., M.J.N., H.P., M.P.-P., V.N.P., R. Pekal, R. Pizzo W.R., H.R., H.J.A.R., A.R., D.J.S., A.S., J.S., O.S., M.S., M.T., M.C.T., A.v.A., R.A.M.J.W., R.J.v.W., O.W., P. Zarka and P. Zucca are members of the LOFAR Builders’s List, and contributed to these results through their efforts in the construction and commissioning of the LOFAR telescope. J.D. contributed through interpretation of the results. All authors approved the final version of the manuscript.

Corresponding authors

Correspondence to B. M. Hare or O. Scholten.

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Supplementary information

Supplementary Information

This is a single document that includes significant additional information on our work. Including: description of our imaging technique, additional information about the 2016 and 2017 lightning flashes, additional needles that were imaged in the 2016 and 2017 flashes, additional hypothesis, discussions on the potential for optical observations of needles, and a simple location error analysis.

Video 1 Lightning: complete rotating

A 3D animation of the 2017 flash.

Video 2 Lightning detail: negative leader

A close-up animation of a negative leader in the 2017 flash.

Video 3 Lightning detail: needle

A close-up animation of a segment of positive leader, with needle N4 shown in red.

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Hare, B.M., Scholten, O., Dwyer, J. et al. Needle-like structures discovered on positively charged lightning branches. Nature 568, 360–363 (2019). https://doi.org/10.1038/s41586-019-1086-6

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