Can irregularities of solar proxies help understand quasi-biennial solar variations?
We define, calculate and analyze irregularity indices λ<sub>ISSN</sub> of daily series of the International Sunspot Number ISSN as a function of increasing smoothing from <i>N</i> = 162 to 648 days. The irregularity indices λ are computed within 4-year sliding wind...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2014-08-01
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| Series: | Nonlinear Processes in Geophysics |
| Online Access: | http://www.nonlin-processes-geophys.net/21/797/2014/npg-21-797-2014.pdf |
| _version_ | 1828196698037420032 |
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| author | A. Shapoval J. L. Le Mouël M. Shnirman V. Courtillot |
| author_facet | A. Shapoval J. L. Le Mouël M. Shnirman V. Courtillot |
| author_sort | A. Shapoval |
| collection | DOAJ |
| description | We define, calculate and analyze irregularity indices λ<sub>ISSN</sub> of
daily series of the International Sunspot Number ISSN as a function of increasing
smoothing from <i>N</i> = 162 to 648 days. The irregularity indices λ are
computed within 4-year sliding windows, with embedding dimensions <i>m</i> = 1 and
2. λ<sub>ISSN</sub> displays Schwabe cycles with
~5.5-year variations ("half Schwabe variations" HSV). The mean of λ<sub>ISSN</sub> undergoes a
downward step and the amplitude of its variations strongly decreases around
1930. We observe changes in the ratio <i>R</i> 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
<i>N</i>. We identify two distinct regimes, called Q1 and Q2, defined mainly by the
evolution of <i>R</i> as a function of <i>N</i>: Q1, with increasing HSV behavior and <i>R</i> value
as <i>N</i> is increased, occurs before 1915–1930; and Q2, with decreasing HSV
behavior and <i>R</i> value as <i>N</i> 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 <i>T</i><sub>1</sub> and <i>T</i><sub>2</sub> (<i>T</i><sub>1</sub> = 11 years, and intermediate <i>T</i><sub>2</sub> is
tuned to mimic quasi-biennial oscillations QBO). The model can generate both
Q1 and Q2 regimes. When <i>m</i> = 1, HSV appears in the absence of <i>T</i><sub>2</sub>
variations. When <i>m</i> = 2, Q1 occurs when <i>T</i><sub>2</sub> variations are present,
whereas Q2 occurs when <i>T</i><sub>2</sub> 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. |
| first_indexed | 2024-04-12T10:06:36Z |
| format | Article |
| id | doaj.art-7a80e32b7ee943f082d8cd757d8bb70e |
| institution | Directory Open Access Journal |
| issn | 1023-5809 1607-7946 |
| language | English |
| last_indexed | 2024-04-12T10:06:36Z |
| publishDate | 2014-08-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Nonlinear Processes in Geophysics |
| spelling | doaj.art-7a80e32b7ee943f082d8cd757d8bb70e2022-12-22T03:37:25ZengCopernicus PublicationsNonlinear Processes in Geophysics1023-58091607-79462014-08-0121479781310.5194/npg-21-797-2014Can irregularities of solar proxies help understand quasi-biennial solar variations?A. Shapoval0J. L. Le Mouël1M. Shnirman2V. Courtillot3IEPT RAS, Profsoyuznaya str. 84/32, 117 997 Moscow, RussiaIPGP, 1 rue Jussieu, 75005 Paris, FranceIEPT RAS, Profsoyuznaya str. 84/32, 117 997 Moscow, RussiaIPGP, 1 rue Jussieu, 75005 Paris, FranceWe define, calculate and analyze irregularity indices λ<sub>ISSN</sub> of daily series of the International Sunspot Number ISSN as a function of increasing smoothing from <i>N</i> = 162 to 648 days. The irregularity indices λ are computed within 4-year sliding windows, with embedding dimensions <i>m</i> = 1 and 2. λ<sub>ISSN</sub> displays Schwabe cycles with ~5.5-year variations ("half Schwabe variations" HSV). The mean of λ<sub>ISSN</sub> undergoes a downward step and the amplitude of its variations strongly decreases around 1930. We observe changes in the ratio <i>R</i> 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 <i>N</i>. We identify two distinct regimes, called Q1 and Q2, defined mainly by the evolution of <i>R</i> as a function of <i>N</i>: Q1, with increasing HSV behavior and <i>R</i> value as <i>N</i> is increased, occurs before 1915–1930; and Q2, with decreasing HSV behavior and <i>R</i> value as <i>N</i> 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 <i>T</i><sub>1</sub> and <i>T</i><sub>2</sub> (<i>T</i><sub>1</sub> = 11 years, and intermediate <i>T</i><sub>2</sub> is tuned to mimic quasi-biennial oscillations QBO). The model can generate both Q1 and Q2 regimes. When <i>m</i> = 1, HSV appears in the absence of <i>T</i><sub>2</sub> variations. When <i>m</i> = 2, Q1 occurs when <i>T</i><sub>2</sub> variations are present, whereas Q2 occurs when <i>T</i><sub>2</sub> 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.http://www.nonlin-processes-geophys.net/21/797/2014/npg-21-797-2014.pdf |
| spellingShingle | A. Shapoval J. L. Le Mouël M. Shnirman V. Courtillot Can irregularities of solar proxies help understand quasi-biennial solar variations? Nonlinear Processes in Geophysics |
| title | Can irregularities of solar proxies help understand quasi-biennial solar variations? |
| title_full | Can irregularities of solar proxies help understand quasi-biennial solar variations? |
| title_fullStr | Can irregularities of solar proxies help understand quasi-biennial solar variations? |
| title_full_unstemmed | Can irregularities of solar proxies help understand quasi-biennial solar variations? |
| title_short | Can irregularities of solar proxies help understand quasi-biennial solar variations? |
| title_sort | can irregularities of solar proxies help understand quasi biennial solar variations |
| url | http://www.nonlin-processes-geophys.net/21/797/2014/npg-21-797-2014.pdf |
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