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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 |
2198-5634
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| Digitales Dokument |
URL |
| Erschienen |
In: Nonlinear Processes in Geophysics Discussions ; 1, no. 1 ; Nr. 1, no. 1 (2014-03-13), S.155-192 |
| Datensatznummer |
250115075
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| Publikation (Nr.) |
 copernicus.org/npgd-1-155-2014.pdf |
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| Zusammenfassung |
| We define, calculate and analyze irregularity indices λWN and
λaa of daily series of sunspot number WN and geomagnetic index
aa 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. λWN and
λaa display Schwabe cycles with sharp peaks not only at cycle maxima
but also at minima: we call the resulting ~5.5 year
variations "half Schwabe variations" (HSV). The mean of λWN 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 WN 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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