Abstract:  This seminar will focus on lightning and transient luminous events in the earth’s atmosphere. Despite over 250 years of research, how lightning originates inside thunderstorms and propagates through air to reach ground is poorly understood. Lightning initiation and propagation involves many physical and chemical processes with very different temporal and spatial scales, making it a very difficult problem to study. On the other hand, lightning-like discharges above thunderstorms, termed transient luminous events, were discovered unexpectedly about twenty-five years ago, including jets, gigantic jets, and sprites. Active research work has since then been carried out to investigate their physical properties and generation mechanisms. In this seminar, we will present our recent optical observations of lightning and transient luminous events. One basic discharge process known as streamers plays a particularly important role in their initiation and propagation. We will also discuss our recent work on streamer modeling.