Magnetic and electric-current helicities in very simple models of the solar dynamo

Xu, Haiqing; Gao, Yu; Попова, Е. П.; Nefedov, S. N.; Zhang, H.; Sokoloff, Dmitry

doi:10.1134/s1063772909020085

Cited by 17 publications

(16 citation statements)

References 9 publications

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“…The twisted magnetic lines of force in the subatmosphere exhibit mirror symmetry relative to the solar equator. It is morphologically consistent with the normal models of a solar dynamo, even if some authors propose reversal mirror‐symmetrical models for studying the helicity formation process at a different phase of the solar cycle (Choudhuri et al 2004; Xu et al 2009; Popova & Nefedov 2010). Fig.…”

Section: Reversal Helicity In the Subatmospheresupporting

confidence: 81%

“…Berger & Ruzmaikin 2000; Kuzanyan, Bao & Zhang 2000; Kleeorin et al 2003; Choudhuri, Chatterjee & Nandy 2004; Zhang et al 2006). In comparison with observational results, the mirror‐symmetrical reverse of the magnetic helicity of solar active regions relative to the preferred hemisphere trends at different phases of the solar cycle has been theoretically demonstrated (Choudhuri et al 2004; Xu et al 2009). A similar simulation for the distribution of current helicity in the full Sun has been provided by Yeates, Mackay & van Ballegooijen (2009).…”

Section: Introductionmentioning

confidence: 82%

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Reversal magnetic chirality of solar active regions and a possible dynamo model

Zhang¹

2011

Monthly Notices of the Royal Astronomical Society

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The transfer of magnetic chirality in solar active regions is related to the emerging magnetic flux ropes generated in the subatmosphere. This analysis has been presented based on the calculation of the injection of magnetic helicity at the solar surface. As the long-term evolution of the accumulated magnetic helicity is followed, it is found that the transfer of reversal magnetic helicity of active regions is a complex process, and is not monotonic with the same sign. It is found that the dominant contribution of helicity occurs mainly in the fast-developing stage of active regions.By considering the hemispheric trends of magnetic helicity, it is proposed that the reversal helicity in solar active regions has two possible causes: local generation in the convection zone, and trans-equatorial processes in the subatmosphere. In addition to the mirror-symmetrical reverse of twisted magnetic field in the convection zone, the possibility of a trans-equatorial process is discussed in this paper.

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Section: Reversal Helicity In the Subatmospheresupporting

confidence: 81%

Section: Introductionmentioning

confidence: 82%

Reversal magnetic chirality of solar active regions and a possible dynamo model

Zhang¹

2011

Monthly Notices of the Royal Astronomical Society

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“…Xu et al, (2009) demonstrated that meridional circulation can be used to make the simulated pattern resemble more closely to what observed (see their Figure 2). Zhang et al (2012) in numerical simulation produced the same type of plots for models based on helicity conservation, to learn that the more or less pronounced migrating pattern is associated with the large-scale magnetic helicity only.…”

Section: Resultsmentioning

confidence: 79%

Current helicity constraints in solar dynamo models

et al. 2012

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Abstract.We investigate to what extent the current helicity distribution observed in solar active regions is compatible with solar dynamo models. We use an advanced 2D mean-field dynamo model with dynamo action largely concentrated near the bottom of the convective zone, and dynamo saturation based on the evolution of the magnetic helicity and algebraic quenching. For comparison, we also studied a more basic 2D mean-field dynamo model with simple algebraic alpha quenching only. Using these numerical models we obtain butterfly diagrams for both the small-scale current helicity and the large-scale magnetic helicity, and compare them with the butterfly diagram for the current helicity in active regions obtained from observations. This comparison shows that the current helicity of active regions, as estimated by −A · B evaluated at the depth from which the active region arises, resembles the observational data much better than the small-scale current helicity calculated directly from the helicity evolution equation. Here B and A are respectively the dynamo generated mean magnetic field and its vector potential.

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“…It is possible that current helicity density as a tracer of the alpha-effect has changed its sign with depth near the bottom of SCZ [29] . There is a phase shift between the magnetic field and the magnetic helicity based on the Parker dynamo theory, and phase shift remains stable with variations of the dynamo models [30] .…”

Section: Discussionmentioning

confidence: 99%

Some basic questions on helicity inferred from vector magnetograms

Gao

Zhang

2009

Sci. China Ser. G-Phys. Mech. Astron.

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This paper summarizes current helicity measurements in the solar active regions (ARs). There is a basic agreement with the "hemispheric sign rule (HSR)" of the current helicity among different vector magnetographs through two solar cycles, but there is a large dispersion of the fraction of ARs following the HSR. In our sample, there are 50%-78% ARs in solar cycle 22 and 44%-79% ARs in cycle 23 following the HSR. A variation is also found in the fraction of the ARs following the HSR between different instruments even when the same ARs are selected. The difference also exists for the same instrument when the selected ARs are different. There are some differences in the variation of HSR with solar cycle for the individual helicity parameter inferred from different instruments. Factors which influence the correlation of different data sets are analyzed.photosphere, magnetic field, helicity, solar dynamo Magnetic (current) helicity provides some information on the chirality and non-potentiality of the magnetic field in the solar atmosphere. Magnetic helicity density is h m = A·∇×A and current helicity density is h c = B·∇×B, where B is magnetic field and A is its vector potential. Most vector magnetographs obtain photospheric vector magnetic fields. As a result, the vertical component B · (∇ × B) of h c in active regions can be obtained (Bao and Zhang [1] ). In a framework of linear force free field ×B = αB, and then we can obtain α=h c /B 2 which can also be used as a helicity proxy. There are generally two methods for calculating α: (1) α best which is a best-fit single value for the whole active region in a least-squares sense [2] ; (2) α av = J z · sign(B z )/ |B z | [3] which is the average value of J z weighed by the ratio of the residual vertical magnetic field to the total unsigned vertical magnetic field.An notable tendency has been found that most active regions (ARs) show negative sign of mean current helicity density in the northern hemisphere and positive one in the southern hemisphere [4] . This tendency is called "hemispheric sign rule (HSR)" of helcity. This is very important for seeking the information of the mirror asymmetry of alpha-effect in solar dynamo theory [5,6] . The results of the current helicity study obtained by pre-

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Magnetic and electric-current helicities in very simple models of the solar dynamo

Cited by 17 publications

References 9 publications

Reversal magnetic chirality of solar active regions and a possible dynamo model

Reversal magnetic chirality of solar active regions and a possible dynamo model

Current helicity constraints in solar dynamo models

Some basic questions on helicity inferred from vector magnetograms

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