%0 Journal Article
%T Can irregularities of solar proxies help understand quasi-biennial solar variations?
%+ Institut de Physique du Globe de Paris (IPGP)
%A Shapoval, A.
%A Le Mouël, J. L.
%A Shnirman, M.
%A Courtillot, V.
%< avec comité de lecture
%@ 1023-5809
%J Nonlinear Processes in Geophysics
%I European Geosciences Union (EGU)
%V 21
%P 797-813
%8 2014
%D 2014
%Z 2014NPGeo..21..797S
%R 10.5194/npg-21-797-2014
%Z Sciences of the Universe [physics]Journal articles
%X We define, calculate and analyze irregularity indices λ_{ISSN} 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. λ_{ISSN} displays Schwabe cycles with ~5.5-year variations ("half Schwabe variations" HSV). The mean of λ_{ISSN} 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 T_{1} and T_{2} (T_{1} = 11 years, and intermediate T_{2} 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 T_{2} variations. When m = 2, Q1 occurs when T_{2} variations are present, whereas Q2 occurs when T_{2} 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.
%G English
%2 https://insu.hal.science/insu-03581114/document
%2 https://insu.hal.science/insu-03581114/file/npg-21-797-2014.pdf
%L insu-03581114
%U https://insu.hal.science/insu-03581114
%~ INSU
%~ UNIV-PARIS7
%~ AFRIQ
%~ CNRS
%~ IPGP
%~ SORBONNE-UNIVERSITE
%~ UNIV-PARIS
%~ SU-TI
%~ ALLIANCE-SU