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| Titel |
Can irregularities of solar proxies help understand quasi-biennial solar variations? |
| VerfasserIn |
A. Shapoval, J. L. Le Mouël, M. Shnirman, V. Courtillot  |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1023-5809
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| Digitales Dokument |
URL |
| Erschienen |
In: Nonlinear Processes in Geophysics ; 21, no. 4 ; Nr. 21, no. 4 (2014-08-01), S.797-813 |
| Datensatznummer |
250120930
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| Publikation (Nr.) |
 copernicus.org/npg-21-797-2014.pdf |
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| Zusammenfassung |
| We define, calculate and analyze irregularity indices λISSN of
daily series of the International Sunspot Number ISSN as a function of increasing
smoothing from N = 162 to 648 days. The irregularity indices λ are
computed within 4-year sliding windows, with embedding dimensions m = 1 and
2. λISSN displays Schwabe cycles with
~5.5-year variations ("half Schwabe variations" HSV). The mean of λISSN undergoes a
downward step and the amplitude of its variations strongly decreases around
1930. We observe changes in the ratio R of the mean amplitude of λ
peaks at solar cycle minima with respect to peaks at solar maxima as a
function of date, embedding dimension and, importantly, smoothing parameter
N. We identify two distinct regimes, called Q1 and Q2, defined mainly by the
evolution of R as a function of N: Q1, with increasing HSV behavior and R value
as N is increased, occurs before 1915–1930; and Q2, with decreasing HSV
behavior and R value as N is increased, occurs after ~1975. We
attempt to account for these observations with an autoregressive (order 1)
model with Poissonian noise and a mean modulated by two sine waves of
periods T1 and T2 (T1 = 11 years, and intermediate T2 is
tuned to mimic quasi-biennial oscillations QBO). The model can generate both
Q1 and Q2 regimes. When m = 1, HSV appears in the absence of T2
variations. When m = 2, Q1 occurs when T2 variations are present,
whereas Q2 occurs when T2 variations are suppressed. We propose that the
HSV behavior of the irregularity index of ISSN may be linked to the presence of
strong QBO before 1915–1930, a transition and their disappearance around
1975, corresponding to a change in regime of solar activity. |
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