Earth-Ionosphere Cavity Resonator

Abstract

The electrically non-conductive air layer bordered by the highly conductive surface of the Earth and the highly conductive but dissipative ionosphere forms a spherical cavity resonator for the wavelengths comparable with the circumference of the Earth. These wavelengths are in the lowest frequency range (<100 Hz) of the ELF (Extremely Low Frequency) band (3 Hz - 3 kHz). These waves can circumnavigate around the Earth before the attenuation. The phase addition and cancellation can produce resonant line spectrum at ∼8, ∼14, ∼20, ∼26 Hz, etc. in the multiple propagation path. The time need for the attenuation is about 0.5 sec in case of 8 Hz. The lightning impulses occurring in 40-50/sec assures the continuous excitation of the Earth-ionosphere cavity. The resonance phenomenon is known as Schumann resonance (SR, cf. Schumann 1952) and can be considered as a natural and cheap investigation tool for studying global changes. Its integrative ability can give robust estimation on the global changes of climate in the troposphere by the space and time variation of global lightning activity and on the extraterrestrial influences in the ionospheric border-wall of the cavity as well as on the modulation of global lightning attributed to the space weather - Earth weather relationships. The whistlers are special electromagnetic waves also produced by lightning strokes in the VLF (Very Low Frequency) frequency band (3-30 kHz) which can escape from the ionosphere. They are trapped in conductive magnetic tubes and propagate from one hemisphere to the other one in the magnetosphere and can be detected at the conjugate point of the trap location (see Lichtenberger et al. in this issue). First of all this paper summarizes the results based on the SR observation in the Széchenyi István Geophysical Observatory at Nagycenk.