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Singular Spectral Analysis of the aa and Dst Geomagnetic Indices

Abstract : We apply singular spectrum analysis in order to identify trends and quasi-periodic oscillations in the aa and Dst series of geomagnetic activity. We also analyze the sunspot number International SunSpot Number (ISSN) and the number of polar faculae Polar Faculae (PF). Singular spectrum analysis provides the eigenvalues and therefore trends and oscillatory components of the four series. ISSN is dominated by a trend (the Gleissberg cycle), followed by 10.6, 35.5 years, two 8-year components, 21.4 and 5.3 year. aa shows the same trend, a 47-year component, then 10.8, 32.3, 21.8, and a series of three close components at 10.6, 12.2, and 9.2 years, followed by a 6 month seasonal component. PF is dominated by the 20.7-year period, followed by 10.2, 8.3, 41, and 31 years, then a 5.2 year component. Dst is dominated by a trend, then a strong 6-month component; next are found a 47-year component, the 10.6 years and a second seasonal line at 1 year. The 22-, 11-, and 5.5-year components are common to the four indices. These "pseudo harmonic" components are evidence of solar activity. Singular spectrum analysis identifies components that vary in frequency and amplitude. The phase relationships of any two components over time can be studied in detail. An illustration is given by the remarkable phase coherency of the 5.3-year component. But the components are neither truly periodical nor exact multiples of each other. These differences reflect the complex mechanisms that govern solar-terrestrial relationships.
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J. L. Le Mouël, F. Lopes, V. Courtillot. Singular Spectral Analysis of the aa and Dst Geomagnetic Indices. Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2019, 124, pp.6403-6417. ⟨10.1029/2019JA027040⟩. ⟨insu-03586616⟩

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