SUMMARY
Nonlinear time series analysis of data related to the radioactivity profile of a hot spring area can explore the dynamics of the geothermal activities along with other different nonlinear features of the Earth system. However, not much work in this field has been done so far in India. In this paper nonlinear time series analysis of the radioactive gas Radon-222 (222Rn) (time series) data recorded at Bakreswar hot spring area of West Bengal, India during the period 2005-2010 was carried out to investigate the dynamics of the radioactive gas emanation process and its relation with the Earth’s tide. Power spectral density and the Hurst exponents were obtained for the above said time series signal using the nonlinear techniques of Fast Fourier Transform (FFT) and power law scaling relationship. An attempt was also made to understand the system dynamics using the surrogate and truncated data of the original time series as well. The result shows that the seasonal variations of the 222Rn emission from the hot spring is highly influenced by the Earth’s tidal effects, and the same has been confirmed by the power spectral density plot. The estimated Hurst exponent from log p-log f plot reflects the anti-persistent Brownian motion nature of the whole five years recorded data set.