North–South asymmetry of the sunspot indices and its quasi-biennial oscillations

Badalyan, O. G.; Обридко, В. Н.

doi:10.1016/j.newast.2011.01.005

Cited by 40 publications

(28 citation statements)

References 18 publications

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“…These findings can be considered as additional signatures of the North-South (NS) asymmetry in the solar hemispheres evolution (e.g. Badalyan & Obridko 2011). Similarly, in Zolotova & Ponyavin (2007) the described above high-frequency components of the sunspot-area signals decomposed via EMD were found to demonstrate randomly mixed phase behaviour, supporting the general idea that the Northern and Southern solar hemispheres evolve rather differently.…”

Section: Discussionsupporting

confidence: 56%

Hilbert–Huang transform analysis of periodicities in the last two solar activity cycles

Kolotkov

Broomhall

Nakariakov

2015

Mon. Not. R. Astron. Soc.

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We investigated periodicities associated with the last two-and-a-half solar activity cycles with the novel Hilbert-Huang Transform (HHT) method. Raw data signals of five different observational proxies: the 10.7 cm radio flux intensity, the helioseismic frequency shift, and the sunspot area signals recorded from the whole solar disk, and separately from the Northern and Southern hemispheres, were expanded into a set of intrinsic modes with the Ensemble Empirical Mode Decomposition (EEMD) technique. Instant and mean periods of each empirical mode were obtained with the use of the Hilbert transform applied independently to each separate mode. The periodicities were allocated to three distinct groups: short-term variations (with periods shorter than 0.5 yr), quasi-biennial oscillations (with typical periods from 0.5 yr to 3.9 yr), and longer periodicities, e.g. such as the 11 yr cycle. All periodicities detected in the examined solar cycles 22-24 are consistent with the well known results found in the earlier solar epochs. We have demonstrated that the HHT method is an ideal tool for characterising periodicities in the helioseismic data, which are necessarily relatively limited in terms of their time resolution. Periodicities obtained using the helioseismic data are, nevertheless, consistent with those found in other proxies. Since helioseismic oscillations are sensitive to the solar interior, this indicates that the behaviour of surface and atmospheric magnetic activity reflects that of the Sun's internal magnetic field. All identified intrinsic modes are seen to have clear amplitude modulation highly correlated with the 11 yr cycle. This amplitude modulation is most pronounced in the short-period modes. The short-term periodicities were found to be multiples of the shortest period, of 25 d. This ordering of the short-term periodicities is consistent with the previous findings. Signatures of the North-South asymmetry were detected in the individual hemisphere sunspot area indices. Furthermore, evidence of the last "extended" solar minimum was detected too.

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Section: Discussionsupporting

confidence: 56%

Hilbert–Huang transform analysis of periodicities in the last two solar activity cycles

Kolotkov

Broomhall

Nakariakov

2015

Mon. Not. R. Astron. Soc.

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“…Oliver & Ballester (1994) found a wave-type secular trend in the asymmetry of sunspot areas for the epoch of 1874-1989 with southern and northern hemispheres being alternately more active for several solar cycles. Badalyan & Obridko (2011) confirmed this trend and extended it to the 1821-2009 epoch. Zolotova et al (2009) and McIntosh et al (2013) found that the activity cycles in the northern and southern hemispheres keep their phase difference for several cycles with the two hemispheres leading the variations alternately.…”

Section: Introductionsupporting

confidence: 55%

Can the long-term hemispheric asymmetry of solar activity result from fluctuations in dynamo parameters?

Nepomnyashchikh

Mandal

Banerjee

et al. 2019

A&A

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Context. The hemispheric asymmetry of sunspot activity observed possesses a regular component varying on a time scale of several solar cycles whose origin and properties are currently debated. Aims. This paper addresses the question of whether the long-term hemispheric asymmetry can result from random variations of solar dynamo parameters in time and latitude. Methods. Scatter in the observed tilt angles of sunspot groups is estimated to infer constraints on fluctuations in the dynamo mechanism for poloidal field regeneration. A dynamo model with fluctuations in the Babcock-Leighton type α-effect is designed in accordance with these constraints and then used to compute a large number of magnetic cycles for statistical analyses of their hemispheric asymmetry.Results. Hemispheric asymmetry in the simulated dynamo results from the presence of an equator-symmetric part in the oscillating magnetic field. The subdominant quadrupolar oscillations are stochastically forced by dominant dipolar oscillations via the equatorsymmetric part of the fluctuating α-effect. The amplitude and sense of the asymmetry of individual cycles varies on a time scale of the order of four dynamo-cycle periods. The variations are irregular, i.e. not periodic. The model suggests that asymmetry in the polar magnetic fields in the solar minima can be used as a precursor for asymmetry of sunspot activity in the following solar cycle.

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“…The seismic quasi‐biennial signal that we observe is highly correlated with the ‘quasi‐biennial oscillation’ (QBO) associated in other proxies of the Sun’s activity (e.g. Kane 2005; Li et al 2006; Ivanov 2007; Vecchio & Carbone 2009; Zaqarashvili et al 2010; Badalyan & Obridko 2011), and here we refer to the quasi‐biennial signal observed in the p‐mode frequencies as the ‘seismic’ QBO. We note here that the QBO observed in other proxies of the Sun’s activity has previously been used to refer to signals with periodicities ranging from 1 to 3 yr.…”

Section: Introductionmentioning

confidence: 57%

Quasi-biennial variations in helioseismic frequencies: can the source of the variation be localized?

Broomhall

Chaplin

Elsworth

et al. 2011

Monthly Notices of the Royal Astronomical Society

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We investigate the spherical harmonic degree (l) dependence of the ‘seismic’ quasi‐biennial oscillation (QBO) observed in low‐degree solar p‐mode frequencies, using Sun‐as‐a‐star Birmingham Solar Oscillations Network data. The amplitude of the seismic QBO is modulated by the 11‐yr solar cycle, with the amplitude of the signal being largest at solar maximum. The amplitude of the signal is noticeably larger for the l= 2 and 3 modes than for the l= 0 and 1 modes. The seismic QBO shows some frequency dependence but this dependence is not as strong as observed in the 11‐yr solar cycle. These results are consistent with the seismic QBO having its origins in shallow layers of the interior (one possibility being the bottom of the shear layer extending 5 per cent below the solar surface). Under this scenario the magnetic flux responsible for the seismic QBO is brought to the surface (where its influence on the p modes is stronger) by buoyant flux from the 11‐yr cycle, the strong component of which is observed at predominantly low latitudes. As the l= 2 and 3 modes are much more sensitive to equatorial latitudes than the l= 0 and 1 modes the influence of the 11‐yr cycle on the seismic QBO is more visible in l= 2 and 3 mode frequencies. Our results imply that close to solar maximum the main influence of the seismic QBO occurs at low latitudes (<45°), which is where the strong component of the 11‐yr solar cycle resides. To isolate the latitudinal dependence of the seismic QBO from the 11‐yr solar cycle we must consider epochs when the 11‐yr solar cycle is weak. However, away from solar maximum, the amplitude of the seismic QBO is weak making the latitudinal dependence hard to constrain.

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North–South asymmetry of the sunspot indices and its quasi-biennial oscillations

Cited by 40 publications

References 18 publications

Hilbert–Huang transform analysis of periodicities in the last two solar activity cycles

Hilbert–Huang transform analysis of periodicities in the last two solar activity cycles

Can the long-term hemispheric asymmetry of solar activity result from fluctuations in dynamo parameters?

Quasi-biennial variations in helioseismic frequencies: can the source of the variation be localized?

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