X-rays associated with the stepping of upward negative leaders at the Säntis Tower: Preliminary results

X-rays have been observed in downward cloud-to-ground lightning and rocket-triggered lightning for the case of negative leaders both during the leader stepping and the dart leader phase [1-3]. X-rays have also been observed during the stepping of dart leaders in upward negative lightning flashes [4,5].      

In this study, we present results from three positive upward flashes. The observations consist of the simultaneous records of X-rays, electric current and electric field at 23 m. Observations from a 2D interferometer system are available for two of the flashes while the third flash was captured by a high-speed camera operating at 24 000 frames per second.

We report X-rays recorded during the initial phase of upward negative leader propagation. To the best of our knowledge, this is the first time that such observations are reported in the literature. The observed X-rays are associated with the stepping of upward negative leaders that can be observed both in the electric field and current waveforms. X-rays associated with the very first step of the upward negative leader were observed in one of the three flashes.

These observations are important to understand the initiation of upward lightning and the mechanisms involved in the initial breakdown.          

[1] Moore, C. B., Eack, K. B., Aulich, G. D., & Rison, W. (2001). Energetic radiation associated with lightning stepped-leaders. Geophysical Research Letters, 28(11), 2141–2144. https://doi.org/10.1029/2001gl013140

[2] Dwyer, J. R. (2003). Energetic Radiation Produced During Rocket-Triggered Lightning. Science, 299(5607), 694–697. https://doi.org/10.1126/science.1078940

[3] Bowers, G. S., Smith, D. M., Martinez‐McKinney, G. F., Kamogawa, M., Cummer, S. A., Dwyer, J. R., Wang, D., Stock, M., & Kawasaki, Z. (2017). Gamma Ray Signatures of Neutrons From a Terrestrial Gamma Ray Flash. Geophysical Research Letters, 44(19). https://doi.org/10.1002/2017gl075071

[4] Hettiarachchi, P., Cooray, V., Diendorfer, G., Pichler, H., Dwyer, J., & Rahman, M. (2018). X-ray Observations at Gaisberg Tower. Atmosphere, 9(1), 20. https://doi.org/10.3390/atmos9010020

[5] Sunjerga, A., Hettiarachchi, P., Smith, D., Rubinstein, M., Cooray, V., Azadifar, M., Mostajabi, A., & Rachidi, F. (2021). X-rays observations at the Santis Tower: Preliminary results. Copernicus GmbH. https://doi.org/10.5194/egusphere-egu21-9586