Lightning to tall structures: Characterization, Modeling and Protection

Lightning physics is highly multidisciplinary, involving areas such as plasma physics, electrical engineering, meteorology, thermodynamics and particle physics. Upward lightning is a special type of lightning initiated from tall structures that has attracted a great deal of interest recently due to growing heights of structures such as wind turbines. Understanding upward lightning is important first to better understand the physics of lightning initiation and development, both in upward and downward flashes as they share similar properties, but also for lightning protection studies. The aim of this thesis is to provide answers to some of the open questions both concerning the mechanisms involved in the lightning process and lightning protection. In the scope of this thesis, we have expanded and upgraded the lightning observation facility at the Säntis Tower that has been instrumented for lightning measurements since 2010. We have in-stalled specific sensors in different frequency bands at different locations to obtain broadband measurements that can give us more insights into the mechanisms involved in the initiation of up-ward lightning flashes from the tower. The new installations include electric field sensors, x-rays sensors, high-speed cameras, and high-resolution cameras. During the summer season of 2019 and 2021, an interferometer system belonging to New Mexico Tech (New Mexico Institute of Mining and Technology) was installed in proximity of the tower capable of reconstructing the lightning path with spatial resolution in the order of one meter and temporal resolution of less than a microsecond. Simultaneous observational data were used to characterize upward lightning. Based on the lightning mapping array observations, we have studied different mechanisms of triggering upward lightning. Typical scenarios leading to the initiation of upward lightning by preceding nearby lightning events are presented and analyzed. Furthermore, we used high-speed camera observations to study the role of recoil leaders in fast subsequent events occurring in upward negative flashes. We observed that all different fast subsequent processes occurring in upward negative lightning are originated from recoil leaders. For the first time, we have explained theoretically the mechanism behind the initiation of upward lightning triggered by nearby lightning activity as observed at the Säntis Tower and other upward lighting observational sites around the world. The developed theoretical model is based on a simplified geometry, and analytical expressions were derived to evaluate the upward leader initiation criteria as a function of geometrical and electrical properties of nearby lightning events. The pro-posed analytical model was further used to estimate the incidence of upward lightning. We showed that the number of upward flashes triggered by nearby lightning can be significantly underestimated by use of empirical formulas proposed in standards. Using a full-wave ap