Schumann resonance is related to stationary (or background) world-wide thunderstorm activity and simultaneously to global properties of the lower ionosphere. This resonance phenomenom is shown to be used as a global thermometer for global warming study.

Transient events in the ELF/VLF range are another important aspect. These non-stationary signals are natural impulsed radio signals, which can be used to study cloud-to-ionosphere discharge (or mesospheric opitcal emissions) (red sprites, blue jets etc.). Clarification of the underlying physical ideas and their practical applications to this pioneering field are emphasized.