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This is the so-called Southern Oscillation Index (SOI). SOI is a climatic index connected with the recurring El NiÑo conditions in the tropical Pacific; it is essentially the normalized monthly mean difference in sea-level pressure between Darwin, Australia and Tahiti (Rasmusson et al., 1990).
Using a convinient graphical user interface you can perform singular-spectrum analysis on input data.

SSA reconstructions of selected components and tests for the presence of trend and oscillatory components are provided. Ad hoc and Monte Carlo error bars for the SSA eigenspectra are also included. All results are displayed graphically. The next figure shows SSA eigenspectrum for the SOI time series:

In addition, the Toolkit includes three kinds of power-spectrum estimation. These are the traditional Blackman-Tukey windowed correlogram, multi-taper method(MTM), and maximum-entropy method(MEM). You can apply these tools at any point in the analysis to a raw time series, or to SSA reconstructions. Outputs include power spectra and significance tests for correlogram and MTM.
The next figure shows MTM spectrum for the same data. The black peaks are components of the spectrum associated with a periodic signal, and the significance levels relative to the estimated noise background are shown.

Colebrook, J.M., 1978:
Continuous plankton records - zooplankton and environment,
northeast Atlantic and North Sea, 1948-1975,
Oceanol. Acta ,1, 9-23.M. Grigorov, 2006: Global dynamics of biological systems from
time-resolved omics experiments, Bioinformatics, 22 (12), 1424--1430.
Mineva A, Popivanov D, 1996: Method of singletrial readiness potential
identification, based on singular spectrum analysis.
J. Neurosci. Methods, 68, 91-99.
Rodo X, Pascual M, Fuchs G, Faruque ASG, 2002:
ENSO and cholera: A nonstationary link related to climate change?
Proc. Nat. Acad. Sci. USA, 99 (20), 12901-12906.
1. NSF ATM 00-82131, Climate System Dynamics on Long Time Scales, U.S. National Science Foundation (ATM + OCE + Math Divisions), 2000--2007.
2. DOE Grant No. DE-FG-020-01ER63251, Predictive Understanding of the Oceans' Wind-Driven Circulation on Interdecadal Time Scales, Office of Science (BER) of the U.S. Department of Energy, 2004--2007.
3. DOE Grant No. DE-FG02-07ER64439,Collaborative Research: Robust Climate Projections and Stochastic Stability of Dynamical Systems , Office of Science (BER) of the U.S. Department of Energy, 2007--2010.
Copyright © SSA-MTM group, (mostly) UCLA.