There are all sorts of interesting phenomena associated with lightning and one of them is called a sprite or red sprite. There’s a list of cool things associated with upper-atmospheric lightning (e.g., see example image, courtesy of Wikimedia Commons at https://en.wikipedia.org/wiki/File:Upperatmoslight1.jpg).
Sprites tend to result from positive cloud-to-ground lightning (i.e., a net positive charge is transferred to the ground from a cloud) [e.g., see Contreras-Vidal et al., 2021], though they can occur after negative cloud-to-ground lightning too [e.g., see Fullekrug et al., 2019]. Their typical red color comes from excitation of nitrogen, though some examples of a green afterglow have been observed suggesting excited oxygen as well.
How does this phenomenon actually occur? What are the physics behind it?
The general consensus is that there’s either a strong return stroke or some other type of electrostatic discharge resulting in charged particles propagating into the upper atmosphere. These collide with existing neutral particles (e.g., nitrogen) and either ionize or excite them, which results in the visible light emissions.
Unfortunately, these phenomena occur in a really tough range of altitudes that make it difficult to examine with in situ measurements. It’s not impossible, but since they are very transient phenomena, launching 100s of rockets in the hopes of coincidentally catching one in the act is generally not feasible. Thus, much is learned from being clever with remote observations of electric, magnetic, and optical observations.
