Figure 8. a) Distribution of time intervals between pulses in
leader A (UUL) and leader B (UCL); b) peak current of pulses occurring
during the initiation and progression of the leaders.
Summary and Conclusion
In this study, for the first time, the current was measured
simultaneously in two upward and competing leaders during the attachment
process of a downward negative leader. The connection took place with
the lightning rod of a residential building and was simultaneously
recorded with high-speed cameras, electric field sensor and current
sensors giving the opportunity to compare the time interval between
current pulses, the amplitude of the pulses and the behavior of the DC
currents of an UCL and an UUL leader.
The approach of the negative downward leader induced 6 upward leaders
prior to the return stroke. The brightest and longest ones were
initiated from instrumented lighting rods and had their current
intensities measured. One of them (from structure B, building P2)
connected to the downward leader.
The downward leader and upward leaders A and B propagated at a constant
speed, being the downward leader 2.0 to 5.5 times faster than the upward
leaders and the UCL 17% faster than the UUL. The final jump speed
(upward and downward leaders combined) is estimated to be at least 45
times faster than the average speed of the UCL prior to the jump.
Although the peak current of the return stroke in this case was much
higher than the previous ones analyzed by Saba et al. (2017) (Table S1
in Supplementary Information), the speed ratios
(Vd/Vucl and
Vd/Vuul) were similar. However, the
charge of the downward leader, which is related to the intensity of the
return stroke, may have influenced the speed of the upward leaders (all
of them faster than previously reported cases). The faster speeds of the
downward leader and the upward connecting leader reduced the time
interval between the UCL leader inception and return stroke. The
distance between the down-coming negative leader tip and the tip of the
vertical rod at the inception of a stable upward positive leader (102 m)
was not significantly different from previous cases (82, 120 and 62 m).
DC currents were measured during the propagation of both leaders (A and
B). Both increased exponentially with a similar growth predicted by
Becerra and Cooray (2009). The DC current of leader B (UCL) was much
more intense than the DC current of leader A (UUL).
Pulses superimposed on the DC current of the upward leader were reported
before. Although the amplitudes of the pulses are different in the case
of taller structures (Visacro et al., 2010, tower height of 60 m over a
300 m tall mountain), the pattern of the pulses observed in this case is
very similar to current measurements of UUL reported from tall towers
(e.g. Figure 8 in Visacro et al., 2010), and from small structures
(Figure 6 in Schoene et al., 2008, grounded vertical conductor of 7 m
height over a flat terrain). Multiple current pulses occur from the
lightning rods during the approach of the negative downward leader and
the amplitude of the current pulses tend to increase with time; the
current peaks of the superimposed leader pulses range from 18 A to 413
A; the pulses superimposed on UCL leaders are larger than the pulses
superimposed on UUL leaders.
The average time interval between current pulses in upward leaders is
close to the interstep time interval found by optical or electric field
sensors for negative cloud-to-ground stepped leaders, which strongly
suggests that the current pulses present in upward leaders are induced
by the electric field change produced by the steps in the propagation of
the negative downward leader
The upward leaders A and B respond to different downward propagating
branches and, as the branches alternate in propagation and intensity, so
do leaders A and B accordingly. During the last 100 µs there is a rapid
exponential growth of the DC base current, the alternation of the
leaders ceases, all downward leader branches intensify and consequently
leaders A and B synchronize and pulse together.
Although the leaders have a constant speed, their linear charge density
increases rapidly during their propagation. The total charge of the UCL
is 5 times larger than the total charge of the UUL. The average linear
densities for upward leaders (49 and 82 µC/m) were obtained for the
first time for natural lightning. Previous measurements and estimations
(from triggered lightning, laboratory measurements and theoretical
studies) show values that range from half to 4 times higher.
The identification and characterization of the UCL and UUL reported here
can help not only the understanding of the attachment process when
several upward leaders are induced, but also the impact of these upward
leaders in vulnerable equipment, in the ignition of flammable vapors and
in injures caused to humans (Schoene et al., 2008; Becerra and Cooray,
2009).
Acknowledgements
The authors would like to thank Lie Bie (Benny), Raphael B. G. Silva,
Marco A. S. Ferro, Hugh Hunt, Guilherme Aminger, and Eliah Fernanda S.
Sabbas for all support in equipment installation and data acquisition.
We also thank Dr. Alexandre Piantini, Dr. Acácio Silva Neto, Dr. Celso
Pereira Braz and staff from the high-voltage facility at the Institute
of Energy and Environment (IEE) at the University of S. Paulo, Brazil
for the calibration tests of the current transformer sensor. This work
was supported by research grants from FAPESP (Project 2012/15375-7);
CNPq (Projects 141450/2021-5, 153799/2022-6).
Data Availability Statement
The high-speed videos analyzed in this work are available at:
https://doi.org/10.5281/zenodo.7244891
References
Arcanjo, M., Guimarães, M., & Visacro, S. (2019). On the interpeak
interval of unipolar pulses of current preceding the return stroke in
negative CG lightning. Electric Power Systems Research ,173 (March), 13–17. https://doi.org/10.1016/j.epsr.2019.03.028
Becerra, M., & Cooray, V. (2009). On the interaction of lightning
upward connecting positive leaders with humans. IEEE Transactions
on Electromagnetic Compatibility , 51 (4), 1001–1008.
https://doi.org/10.1109/TEMC.2009.2033265
Chen, M., Zheng, D., Du, Y., & Zhang, Y. (2013). Evolution of line
charge density of steadily-developing upward positive leaders in
triggered lightning. Journal of Geophysical Research Atmospheres ,118 (10), 4670–4678. https://doi.org/10.1002/jgrd.50446
Hill, J. D., Uman, M. A., & Jordan, D. M. (2011). High-speed video
observations of a lightning stepped leader. Journal of Geophysical
Research Atmospheres , 116 (16), 1–8.
https://doi.org/10.1029/2011JD015818
Krider, E. P., Weidman, C. D., & Noggle, R. C. (1977). The electric
field produced by lightning stepped leaders. Journal of
Geophysical Research . https://doi.org/10.1029/jc082i006p00951
Lu, W., Chen, L., Ma, Y., Rakov, V. A., Gao, Y., Zhang, Y., et al.
(2013). Lightning attachment process involving connection of the
downward negative leader to the lateral surface of the upward connecting
leader. Geophysical Research Letters , 40 , 5531–5535.
https://doi.org/10.1002/2013GL058060
Lu, W., Gao, Y., Chen, L., Qi, Q., Ma, Y., Zhang, Y., et al. (2015).
Three-dimensional propagation characteristics of the leaders in the
attachment process of a downward negative lightning flash. Journal
of Atmospheric and Solar-Terrestrial Physics , 136 , 23–30.
https://doi.org/10.1016/j.jastp.2015.07.011
Naccarato, K. P., Saraiva, A. C. V., Saba, M. M. F., & Schumann, C.
(2012). First Performance Analisys of BrasilDAT Total Lightning Network
in Southeastern Brazil. In International Conference on Grounding
and Earthing & 5th International Conference on Lightning Physics and
Effects (p. 6). Bonito.
Naccarato, K. P., De Paiva, A. R., Saba, M. M. F., Schumann, C., Silva,
J. C. O., & Ferro, M. A. S. (2017). Preliminary comparison of direct
electric current measurements in lightning rods and peak current
estimates from lightning location systems. 2017 International
Symposium on Lightning Protection, XIV SIPDA 2017 , (October), 319–323.
https://doi.org/10.1109/SIPDA.2017.8116944
Nag, A., Cummins, K. L., Plaisir, M. N., Wilson, J. G., Crawford, D. E.,
Brown, R. G., et al. (2021). Inferences on upward leader characteristics
from measured currents. Atmospheric Research , 251 (November
2020), 105420. https://doi.org/10.1016/j.atmosres.2020.105420
Les Renardières, G. (1977). Positive discharges in long air gaps at Les
Renardières - 1975. Electra , 53 .
Rizk, F. A. M. (1990). MODELING OF TRANSMISSION LINE EXPOSURE TO
DIRECT LIGBTNING STROKES . IEEE Transactions on Power Delivery(Vol. 5).
Rizk, F. A. M. (1994). Modeling of Lightning Incidence to Tall
Structures Part I: Theory. IEEE Transactions on Power Delivery ,9 (1).
Saba, M. M. F., Schumann, C., Warner, T. A., Helsdon, J. H., & Orville,
R. E. (2015). High-speed video and electric field observation of a
negative upward leader connecting a downward positive leader in a
positive cloud-to-ground flash. Electric Power Systems Research ,118 , 89–92. https://doi.org/10.1016/j.epsr.2014.06.002
Saba, M. M. F., Paiva, A. R., Naccarato, K. P., Siqueira, F. V. C.,
Sabbas, F. S., Silva, J. C. O., et al. (2017). Current measurements of
upward leaders from buildings. 2017 International Symposium on
Lightning Protection (XIV SIPDA) , (October), 2–5.
Saba, M. M. F., Ferro, M. A. S., Cuadros, E. T., Custódio, D. M., Nag,
A., Schumann, C., et al. (2019). High-Speed Video Observation of a Dart
Leader Producing X-rays. Journal of Geophysical Research: Space
Physics , 124 (12), 10564–10570.
https://doi.org/10.1029/2019JA027247
Schoene, J., Uman, M. A., Rakov, V. A., Jerauld, J., Hanley, B. D.,
Rambo, K. J., et al. (2008). Experimental Study of Lightning-Induced
Currents in a Buried Loop Conductor and a Grounded Vertical Conductor.IEEE Transactions on Electromagnetic Compatibility , 50 ,
110–117. https://doi.org/10.1109/TEMC.2007.911927
Visacro, S., Murta Vale, M. H., Correa, G., & Teixeira, A. (2010).
Early phase of lightning currents measured in a short tower associated
with direct and nearby lightning strikes. Journal of Geophysical
Research , 115 (D16104), 1–11.
https://doi.org/10.1029/2010JD014097
Visacro, S., Guimaraes, M., & Murta Vale, M. H. (2017). Features of
Upward Positive Leaders Initiated From Towers in Natural Cloud-to-Ground
Lightning Based on Simultaneous High-Speed Videos, Measured Currents,
and Electric Fields. Journal of Geophysical Research:
Atmospheres , 122 , 12,786-12,800.
https://doi.org/10.1002/2017JD027016