Fourier and wavelet analyses of climate data

In this paper, we report a case study, addressed to scientific curricula graduate students, concerning the application of Fourier Transform (FT) and Wavelet Transform (WT) on climate data and on their connections with Milankovitch's cycles. It is shown how, contrarily to FT that furnishes only the signal frequency values, WT allows to get information on the time evolution of the frequencies content. From the performed FT and WT analyses the presence of glacial maxima with time intervals of around 100000 years emerges. These have been connected with the variation of the eccentricity of the Earth's orbit. Moreover, between 1.8 and 1.3 million years ago, glacial maxima repeat about every 41.000 years in agreement with the cycle of variation of the Earth's axis inclination