Insights into High Peak Current In-cloud Lightning Events during Thunderstorms

Abstract:

With the goal of understanding the nature of very high peak current IC lightning events, we investigated National Lightning Detection Network reports and lightning radio waveforms recorded by Duke magnetic field network in a 44-day observation period to analyze the in-cloud (IC) events producing currents above 200 kA. We find two distinct classes of IC lightning events with very high peak currents: the well-known but poorly understood narrow bipolar events (NBEs), and a previously unreported type that we call energetic in-cloud pulses (EIPs). Positive and negative EIPs produce slower radiation waveforms that occur in a very different lightning context comparing with NBEs. That context shows that EIPs are generated from existing negative polarity leaders that are propagating usually upward but sometimes downward. Specifically, positive EIPs are generated during upward negative leaders at the altitude of 10 – 13 km, while negative EIPs are observed during the early stages of downward negative leader processes. It is very interesting to note that the characteristics of EIPs and some previously reported terrestrial gamma ray flashes (TGFs) associated events are nearly identical. This may indicate a connection between EIPs and TGFs that requires more investigation. Our measurement also indicate the comparable radiation field of these very high peak current IC events and strong cloud-to-ground strokes, which may suggest the possible association of EIPs with ionospheric perturbations and optical emissions known as elves.