Indian monsoon rainfall is higher in epochs of higher solar activity: a wavelet cross-spectral analysis

Using the Morlet continuous wavelet transform on data over the period 1871-1990, it is found that the global wavelet cross spectra between two solar activity indices and seven major Indian monsoon rainfall time series show significant power around the period of the 11 year solar cycle, passing the $\chi^2$ test of significance proposed by Torrence and Compo (1998) at levels exceeding 95% in 10 out of the 14 cases studied. Furthermore two distinct epochs are found in the computed cross-spectrum, the transition between them occurring around the decade 1915-1925, beyond which solar activity parameters show a significant increase. By comparison between selected periods of three cycles in solar activity in each of the two epochs, it is shown that the average rainfall is higher in all seven rainfall indices during periods of greater solar activity, at {\it z}-test confidence levels of 95% or greater in three of them.