This study presents and discusses the results of soil radon monitoring at three different volcano sites and one reference site, from December 2007 to January 2009. This relates to the activity of the Popocatepetl Volcano and a radon survey and gamma-ray spectrometry in the area between Paso de Cortes and Tlamacas Mountain, and in the adjacent regions. The results are applied to the aspects of atmosphere electricity and lithosphere-atmosphere coupling in relation to the forecasting of volcano and earthquake activity. The monitoring of radon release reveals a decrease in radon concentration (down to total suppression) with approaching moderate volcanic eruptions. The behavior of the radon activity at the Tlamacas site is more apparent, compared to other observational sites. The average level of radon release observed at the Tlamacas site is much higher, with some characteristic variations. Both the radon survey and gamma-ray spectrometry indicate intensive diffusion radon emission localized in the area of Tlamacas Mountain. The average radon concentration in the area of Tlamacas is about 10-20-fold greater than the background volcano values. The new concept of lithosphere-atmosphere coupling is presented: intensive radon release in high elevated areas shortens and modifies the Earth-to-thunderclouds electric circuit, which provokes microdischarges into the air close to the ground, attracting lightning discharges. This concept attempts to explain in a new way the noise-like geomagnetic emissions registered before major earthquakes, and it promotes interest for the study of thunderstorm activity in seismo-active zones, as a promising instrument for earthquake forecasting.

Modulation of magnetic components of ULF Alfve´n wave (f=0.02–2 Hz), which is incident from the magnetosphere to the Earth’s surface, is considered. This modulation is due to variations of electron and ion concentrations within the ionosphere F-layer caused by acoustic-gravity waves or internal gravity waves of ULF (0.0005–0.02 Hz) range. The maximum modulation of the magnetic field at the Earth’s surface takes place when maximum variations of the electron concentration are observed at altitudes 225–275 km. The modulation is more essential when the inclination angle of the geomagnetic field is Z501. The 20% modulation of the electron concentration results in the magnetic field modulation at the Earth’s surface of 30–40%. At the frequencies f1 Hz there exists the resonant modulation when in the narrow (0.1 Hz) frequency range the modulation increases sharply. The results can explain the ground-based observations of generation of the seismo-related ULF magnetic perturbations.