Interferometric imaging of Intensely Radiating Negative Leaders

• Main Authors: Scholten, Olaf, Hare, Brian M, Dwyer, Joe, Liu, Ningyu, Sterpka, Chris, Kolmasov, Ivana, Santolik, Ondrej, Lan, Radek, Uhlir, Ludek, Buitink, Stijn, Huege, Tim, Nelles, Anna, ter Veen, Sander
• Format: Journal Article
• Language: English
• Published: 06-10-2021
• Subjects: Physics - Atmospheric and Oceanic Physics; Physics - Instrumentation and Methods for Astrophysics
• DOI: 10.48550/arxiv.2110.02547

Phys Rev D 105, 062007 (2022) The common phenomenon of lightning still harbors many secrets and only
recently a new propagation mode was observed for negative leaders. While
propagating in this `Intensely Radiating Negative Leader' (IRNL) mode a
negative leader emits 100 times more very-high frequency (VHF) and broadband
radiation than a more normal negative leader. We have reported that this mode
occurs soon after initiation of all lightning flashes we have mapped as well as
sometimes long thereafter. Because of the profuse emission of VHF the leader
structure is very difficult to image. In this work we report on measurements
made with the LOFAR radio telescope, an instrument primarily built for
radio-astronomy observations. For this reason, as part of the present work, we
have refined our time resolved interferometric 3-Dimensional (TRI-D) imaging to
take into account the antenna function. The images from the TRI-D imager show
that during an IRNL there is an ionization front with a diameter in excess of
500~m where strong corona bursts occur. This is very different from what is
seen for a normal negative leader where the corona bursts happen at the tip, an
area of typically 10~m in diameter. The observed massive ionization wave
supports the idea that this mode is indicative of a dense charge pocket.