Title:

Automated Classification Of Narrow Bipolar Pulses

A narrow bipolar event (NBE) is a uniquely high-power, electrical discharge that takes places within thunderclouds [1]. "They are the most powerful terrestrial source of high‐frequency (HF) and very high frequency (VHF) electromagnetic radiation in nature [2]", there is evidence that they can initiate other thunderstorm electrical discharges [2], and the polarity of their sferics (i.e., broadband electromagnetic signals) may correlate with the physical intensity of the storm [1]. These unique properties incentivize the identification and categorizing of NBEs for use in further research. In this work, we develop a method to automatically identify NBEs and determine their breakdown polarity using the INTF dataset, which consists of measurements from three broadband VHF (20-80 MHz) radio receivers that are used for interferometry, and a single electric-field change antenna that is used to record sferics produced by lightning. The INTF array was deployed to Kennedy Space Center in 2016, and all four signals were synchronously-digitized at 180 MSps. In our approach, NBEs are identified based on their narrow (roughly 10 microsecond-wide) bipolar sferics, and then the corresponding VHF data is processed to determine the breakdown polarity of the event. [1] Wu, T., Takayanagi, Y., Yoshida, S., Funaki, T., Ushio, T., and Kawasaki, Z. ( 2013), Spatial relationship between lightning narrow bipolar events and parent thunderstorms as revealed by phased array radar, Geophys. Res. Lett., 40, 618– 623. [2]  Liu, N., Dwyer, J. R., Tilles, J., Stanley, M. A., Krehbiel, P. R., Rison, W., et al. ( 2019). Understanding the radio spectrum of thunderstorm narrow bipolar events. Journal of Geophysical Research: Atmospheres, 124, 10134– 10153.

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