Speaker: Richard Sonnenfeld

Affiliation: New Mexico Tech 

EXPERIMENTAL STUDIES OF LIGHTNING LEADERS IN NATURAL AND TRIGGERED LIGHTNING

Before lightning can happen, a reasonably conductive path to ground (or to different parts of a cloud) must be created.  Streamers are roughly ~10-m segments of air whose ionization is primarily driven by high electric fields.  A fan of streamers can feed current into a leader, whose ionization is primarily driven by temperature.  Over many years of lightning studies, methods have been developed to see and measure leaders and streamers.  In particular, as leaders advance they produce bursts of broadband radio emissions.  These bursts can be located with time of arrival techniques like the lightning mapping array and the lightning interferometer.  At least since the work of Kasimir, it has been recognized that a lightning channel in the clouds has a positive and a negative end. Positive leaders generally emit RF signals that are an order of magnitude smaller than negative leaders.  Further, positive leaders propagate in smaller fields, are slower, and generally dimmer in optical observations.  Despite being difficult to see, positive leaders are practically important to understand  because they are what is typically emitted from lightning rods (and other structures such as wind turbines) before they intercept down-coming leaders.  In recent summers, we have been observing positive leaders from lightning rods, and in summer of 2025, we obtained high speed video of positive leaders from rocket triggered lightning.  Continued analysis of our data should provide insight into lightning ``attachment''.