The universal Rn wave. An approach.
A large set of hourly Rn atmospheric concentration data collected during 1976, 1978, 1979 and 1980 has been obtained. These data follow a log-normal distribution law. The Fourier analysis of the mean daily course of Rn by month (Rn wave) shows that to accurately represent such a wave two terms are sufficient. Assuming that with a great deal of data the influence of the meteorological variables is very low, the two terms have been interpreted taking into account only the atmospheric stability, which depends on the solar flux. By applying the same treatment to Rn concentration data from other sites it was found that: (a) the phase of the first harmonic is a constant, independent of the site; (b) the phase of the second harmonic is a linear function of the hourly difference between sunrise and sunset; (c) the amplitude of the first harmonic is a linear function of the solar flux; and (d) no reliable correlation was found for the amplitude of the second harmonic, for which reason a mean value was taken. The error obtained in the prediction of the Rn wave was tolerable.