Modelling variability of solar activity cycles

Kitchatinov, L. L.; Мордвинов, А. В.; Nepomnyashchikh, Alexander

doi:10.1051/0004-6361/201732549

Cited by 34 publications

(30 citation statements)

References 54 publications

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“…Observations show that many stars show irregular cycles and possibly extended grand minima (Saar & Testa 2012;Wright 2016). Thus the irregular aspects should be carefully studied, and checked whether the solar dynamo models (Karak & Choudhuri 2011;Hazra et al 2015;Kitchatinov et al 2018) which are successful in explaining many irregular aspects of the solar cycle are capable of explaining the irregular features of other stars. However, seeing the success in reproducing many observational features of stellar cycles in our model, we can have some confidence on the basic assumptions made in our model, and we expect that the prediction made on the quadrupolar field in rapidly rotating stars is true.…”

Section: Discussionmentioning

confidence: 99%

Exploring the Cycle Period and Parity of Stellar Magnetic Activity with Dynamo Modeling

Hazra

Jiang

Karak

et al. 2019

ApJ

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Observations of chromospheric and coronal emissions from various solar-type stars show that the stellar magnetic activity varies with the rotation rates of the stars. The faster the star rotates, its magnetic activity gets stronger but activity cycle period does not show a straightforward variation with the rotation rate. For slowly rotating stars, the cycle period decreases with the increase of rotation rate, while for the fast rotators dependency of cycle period on rotation is presently quite complicated. We aim to provide an explanation of these observational trends of stellar magnetic activity using a dynamo model. We construct a theoretical dynamo model for stars of mass 1 M based on the kinematic flux transport dynamo model including radial pumping near the surface of the stars. The inclusion of this near surface downward radial pumping is found to be necessary to match the observed surface magnetic field in case of the Sun. The main ingredients of our dynamo model, meridional circulation and differential rotation for stars are obtained from a mean-field hydrodynamic model. Our model shows a decrease of cycle period with increasing rotation rate in the slowly rotating regime and a slight increase of cycle period with rotation rate for the rapid rotators. The strength of the magnetic field is found to be increasing as the rotation rate of the star increases. We also find that the parity of the stellar magnetic field changes with rotation. According to our model, the parity flips to quadrupolar from dipolar if the rotation period of the star is less than 17 days.

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Section: Discussionmentioning

confidence: 99%

Exploring the Cycle Period and Parity of Stellar Magnetic Activity with Dynamo Modeling

Hazra

Jiang

Karak

et al. 2019

ApJ

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“…The values of σ = 2.7 and τ = 25.4 days are used in the computations of this paper. These values are inferred from sunspot statistics Kitchatinov et al 2018). The value of δθ = 0.1 (≃ 6 • ) is close to the characteristic latitudinal size of sunspot groups.…”

Section: Regular and Fluctuating Parts Of The α-Effectmentioning

confidence: 99%

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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“…Stronger cycles show wider activity belts and thus start to decline earlier than weaker cycles. Nagy et al (2017) and Kitchatinov et al (2018) showed that peculiar BMRs with large tilt angles that emerge during the rising phase of a cycle have large effects on the amplitude of the descending phase. Hence the stochastic mechanism due to random emergence of the peculiar BMRs during the rising phase causes the later phases of the cycle to be noisy, as seen in Figure 5.…”

Section: Properties Of Solar Cycle Profilesmentioning

confidence: 99%

Predictability of the Solar Cycle Over One Cycle

Jiang

Wang

Jiao

et al. 2018

ApJ

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The prediction of the strength of future solar cycles is of interest because of its practical significance for space weather and as a test of our theoretical understanding of the solar cycle. The Babcock-Leighton mechanism allows predictions by assimilating the observed magnetic field on the surface. Since the emergence of sunspot groups has random properties, making it impossible to accurately predict the solar cycle and strongly limiting the scope of cycle predictions, we develop a scheme to investigate the predictability of the solar cycle over one cycle. When a cycle has been ongoing for more than three years, the sunspot group emergence can be predicted along with its uncertainty during the rest time of the cycle. The method for this prediction is to start by generating a set of random realizations that obey the statistical relations of the sunspot emergence. We then use a surface flux transport model to calculate the possible axial dipole moment evolutions. The correlation between the axial dipole moment at cycle minimum and the subsequent cycle strength and other empirical properties of solar cycles are used to predict the possible profiles of the subsequent cycle. We apply this scheme to predict the large-scale field evolution from 2018 to the end of cycle 25, whose maximum strength is expected to lie in the range from 93 to 155 with a probability of 95%.

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Modelling variability of solar activity cycles

Cited by 34 publications

References 54 publications

Exploring the Cycle Period and Parity of Stellar Magnetic Activity with Dynamo Modeling

Exploring the Cycle Period and Parity of Stellar Magnetic Activity with Dynamo Modeling

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

Predictability of the Solar Cycle Over One Cycle

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