The observation of the Earth-ionosphere cavity resonances gives information on the electromagnetic balance of the atmosphere. Lightning flashes within thunderstorms are thought to be the predominant source of excitation of the Earth-ionosphere cavity resonances. Thunderstorms are driven by temperature and moisture conditions and occur predominantly in the tropical belt around the world. Therefore, it has been suggested that an observation of the Earth-ionosphere cavity resonances provides a sensitive measure of the global temperature.
Transient optical emissions in the mesosphere, denoted sprites have been observed in a series of campaigns in the United States since the summer of 1993. Sprites are accompanied by special lightning flashes which represent strong positive cloud-to-ground discharges. They can be observed in the ULF/ELF range as Earth-ionosphere cavity resonances and in the ELF/VLF range as radio atmospherics exhibiting slow-tails.