Interactions and Multifrequency Radiation Characteristics of Bidirectional Leaders in Altitude-Triggered Lightning

Altitude-triggered lightning provides favorable conditions for the research of bidirectional leader system. In the summer of 2023, altitude-triggered lightning experiment was conducted on the Field Experiment Base on Lightning Sciences, China Meteorological Administration. The multifrequency radiation characteristics of bidirectional leaders and the interactions of both ends during the propagation are analyzed. Specifically, the discharge processes relevant to LF-MF magnetic radiations of bidirectional leaders can be revealed by high-speed optical images in altitude-triggered lightning, and all these LF-MF radiations correspond to VHF radiations associated with bidirectional leaders well. Unlike the close correlation between the LF-MF radiation strengths and the discharge intensities, the VHF radiation strengths vary greatly even for similar discharge events, since VHF radiations correspond to microscopic random breakdown processes. Furthermore, the changes of leader speed and channel brightness before and after the bidirectional leaders indicate that the development of the two ends of bidirectional leads is mutually reinforcing.