Indications for solar influence on radon signal in the subsurface of Tenerife (Canary Islands, Spain)

Radon at two locations in Tenerife is investigated. The MM-0 site is located in a bunker near Teide volcano. Daily radon (DR) signals are dominated by a 12-hour (S2) periodicity. Continuous wavelet transform (CWT) analysis of day-time and night-time series results in a day-night differentiation, which does not occur in the coeval temperature and pressure. This indicates that the radon system is directly affected by rotation of Earth around its axis, and not via the pressure and/or temperature pattern. San Fernando sites are in an underground gallery, located at 2.1 and 3 km from the entrance. Alpha and gamma time series show DR signals having an S1 and a strong S2 periodicity. Sidebands occur around the S1 periodicity. The lower sideband is close to 0.9972696 cycles per day (CPD; = sidereal frequency) and the upper sideband at a symmetric frequency above. They reflect a driver containing two waveforms having periodicities of rotation of Earth around its axis and around the Sun that influences radon in a non-linear fashion, leading to the sidebands around the S1 periodicity. Observation in Tenerife of sidebands and day-night phenomena substantiates the notion that the periodic components in the diurnal and annual frequency band of radon time series are due to the influence of a component in solar radiation.