Main reference:
Eduardo Andres Agosta: The 18.6-year nodal tidal cycle and the bi-decadal precipitation oscillation over the plains to the east of subtropical Andes, South America, Int. J. Climatol., 34, 1606-1614, 2014. https://doi.org/10.1002//joc.3787

Eduardo Agosta, on March 17, 2020, sent to me his data relative to the SRI (Summer Rain Index) for the Central West Argentina rainy season (i.e. October to March). Annual data from 1901 (season 1900/01) to 2012 (season 2011/12).

From this dataset I derived MEM Spectra of both 1901-1977 and 1901-2012 series and wavelet spectrum.

FZ 03.04.2020.