Caitano da Silva, Penn State

Title:  Lightning Physics, Related High-Energy Processes, and Their Interactions with the Upper Atmosphere  (Video)

Abstract:  For thousands of years lightning has been one of the most astonishing natural phenomena, being both frightening and fascinating. Lightning is known to play an important role in the atmospheric system: thunderstorms and lightning are the current source for the global electric circuit, lightning is the main non-antropogenic source of nitrogen oxide in the troposphere, and it is believed that lightning contributed to the formation of organic molecules necessary for the formation of life in the early stages of the planet. Concurrently, lightning discharges are known to be a major source of damages for a wide range of objects and systems, including: miniature electronic integrated circuits, overhead and underground electric power and communication systems, buildings, boats, aircrafts, launch vehicles in flight, and forests (i.e., as a source of forest fires). The modern science of lightning and atmospheric electricity is characterized by the emergence of two research areas, as described below.

The first one is concerned with how electricity generated by thunderstorms interacts with the different layers in the atmosphere. The serendipitous discovery of sprites, a lightning-induced electrical discharge in the mesosphere/lower ionosphere, has demonstrated that this region is subject to energy input from below and that thunderstorms may play an active role in the mesospheric chemistry. Today we know that there are several variants of lightning-induced transient luminous events in the middle atmosphere, including sprites, halos, blue jets, gigantic jets, and elves. These phenomena have been shown to be important tools not only to probe the dynamics and composition of the middle atmosphere, but also to characterize the thunderstorms and lightning that generated them in the first place.

The second one investigates high-energy processes associated to lightning and thunderstorms. This research area ignited when a low-orbit satellite aimed to detect gamma-rays from cosmic origin, accidentally identified sources coming from the Earth’s atmosphere below. Twenty years after its discovery, the true physical mechanism of terrestrial gamma ray flashes is still under investigation. Meanwhile, many other aspects of high-energy atmospheric electricity have been determined, such as minute-long gamma-ray glows from thunderstorms and x-rays generated by stepping lightning leaders. The high-energy footprints of lightning and thunderstorms carry very important information on how lightning is initiated inside thunderstorms and on the mechanisms of lightning channel propagation. Their possible deleterious effects on airplanes and crew still have to be quantified. This presentation will provide an overview on recent progress in lightning physics, related high-energy processes, and their interactions with the upper atmosphere.