Solar-Cycle Variation of Magnetic Helicity in Active Regions

Hagino, M.; Sakurai, Takashi

doi:10.1093/pasj/57.3.481

Cited by 76 publications

(66 citation statements)

References 16 publications

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“…More detailed calculations of helicity can be done by using such poloidal field distributions instead of using the simple boundary condition (24). Since some groups have started reporting on the possible cycle variation of helicity on the basis of the observational data (Bao et al 2000;Hagino & Sakurai 2005), such calculations may become relevant in future when more detailed observational data are available.…”

Section: Resultsmentioning

confidence: 99%

Development of twist in an emerging magnetic flux tube by poloidal field accretion

Chatterjee

Choudhuri

Petrovay

2006

A&A

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Aims. Following an earlier proposal for the origin of twist in the magnetic fields of solar active regions, we model the penetration of a wrapped up background poloidal field into a toroidal magnetic flux tube rising through the solar convective zone. Methods. The rise of the straight, cylindrical flux tube is followed by numerically solving the induction equation in a comoving Lagrangian frame, while an external poloidal magnetic field is assumed to be radially advected onto the tube with a speed corresponding to the rise velocity. Results. One prediction of our model is the existence of a ring of reverse current helicity on the periphery of active regions. On the other hand, the amplitude of the resulting twist depends sensitively on the assumed structure (diffuse vs. concentrated/intermittent) of the active region magnetic field right before its emergence, and on the assumed vertical profile of the poloidal field. Nevertheless, in the model with the most plausible choice of assumptions a mean twist comparable to the observations results. Conclusions. Our results indicate that the contribution of this mechanism to the twist can be quite significant, and under favourable circumstances it can potentially account for most of the current helicity observed in active regions.

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Section: Resultsmentioning

confidence: 99%

Development of twist in an emerging magnetic flux tube by poloidal field accretion

Chatterjee

Choudhuri

Petrovay

2006

A&A

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“…Case (b) shows that the sign rule reverses its sense near the activity minimum periods, as was advocated by Hagino & Sakurai (2005). Choudhuri et al (2004) explained such a reversal by the combination of the dynamo-generated new toroidal field and the old poloidal field from the previous cycle.…”

Section: Discussionmentioning

confidence: 76%

“…For reference, Longcope et al (1998) Bao et al (2000) used α best and H c , and Pevtsov et al (2008) used α best . The conclusion of Pevtsov et al (2008), in which Hagino and Sakurai were coauthors, is against Hagino & Sakurai (2005), but the former used α best and the latter adopted α…”

Section: Proxies Of Helicitymentioning

confidence: 99%

“…Bao et al (2000) analyzed many more samples and found that the hemispheric sign rule was satisfied in a sample of 422 regions observed in 1988-1997 (solar cycle 22), but was found violated in a sample of 87 regions observed in 1998-2000 (beginning of cycle 23). Hagino & Sakurai (2005) derived the value of dα/dθ from 1983 to 2002, which should be negative if the hemispheric sign rule holds, and found that the sign of dα/dθ was positive in the period of sunspot number minimum. However, Pevtsov et al (2008) did not find such a systematic change in dα/dθ as a function of time.…”

Section: Introductionmentioning

confidence: 99%

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Magnetic helicity as a probe of magnetic flux-tube dynamics in the solar interior

Sakurai¹,

Gao

Kuzanyan

2012

Proc. IAU

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Abstract. Magnetic helicity (volume integral of the product of the magnetic field vector B and the vector potential A), or its proxy, the current helicity at the surface (surface integral of B · J or Bz Jz ), is an important quantity which characterizes the helical nature of solar magnetic fields. The current helicity on the Sun shows a tendency, though with large dispersion, that it is positive in the southern hemisphere and negative in the northern hemisphere (the helicity sign rule). However, there are indications that the helicity sign rule may be reversed at activity minimum periods. We will discuss the significance of this property by focusing on the statistical distributions of helicity whether its dispersion follows Gaussian distribution or not.

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“…However, the helicity parameter H c shows a weaker opposite hemisphereic preference in the new solar cycle. Hagino and Sakurai (2005) found that although the hemispheric sign rule of helicity generally holds, it is found significant time variations in the yearly values of helicity during the observation period. The hemispheric sign rule of helicity is satisfied in the solar maximum phase, but may not be so in the solar minimum phase.…”

Section: Helicity and Solar Flare-cmesmentioning

confidence: 85%

Helicity of solar magnetic field from observations

Zhang

2009

Proc. IAU

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Abstract. The helicity is an important quantity to present the basic topological configuration of magnetic field transferred form the solar subatmosphere into the interplanetary space. In this paper, we present the observational solar magnetic field and the relationship with the magnetic helicity.Keywords. Sun: magnetic fields, helicity, interior; turbulence, MHD Importance and definition of magnetic helicityHelicities are topologically a measure of the structural complexity of the corresponding fields. Woltjer (1958) presented the basic properties of magnetic helicity firstly. As indicated by Taylor (1986) that the topological invariants of ideal plasma so that only total magnetic helicity survives. Helicity is described in terms of the internal structure of a flux tube and the external relations between flux tubes. The helicity of open field configurations not bounded by magnetic surfaces is discussed by Berger and Field (1984), and a measure of the propagation of topological structures across open boundaries is given also. Pouquet, Frisch, and Leorat (1976) indicated that the turbulence and magnetic fields are a common feature of many celestial bodies. The study confirms the importance of helicity both in its kinetic and in its magnetic form for generation of large-scale magnetic fields by turbulence. Keinigs (1983) and Keinigs and Gerwin (1986) analyzed that in a magnetized plasma the alpha effect represents a turbulently generated emf directed along the mean magnetic field. The alpha effect is reevaluated in terms of ensemble-averaged properties of the magnetic fluctuation spectrum. The results indicate that the turbulent current helicity must be opposite in sign to the mean-field current helicity in order for the alpha effect to play a role in overcoming the resistive diffusion of large-scale magnetic fields. Kleeorin and Rogachevskii (1999) analyzed the evolution of the magnetic helicity tensor for a nonzero mean magnetic field and for large magnetic Reynolds numbers in an anisotropic turbulence.The magnetic helicity density h m =A · B, with A the vector potential for magnetic field B, measures the chirality of magnetic lines of force. The magnetic helicity is defined as

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Solar-Cycle Variation of Magnetic Helicity in Active Regions

Cited by 76 publications

References 16 publications

Development of twist in an emerging magnetic flux tube by poloidal field accretion

Development of twist in an emerging magnetic flux tube by poloidal field accretion

Magnetic helicity as a probe of magnetic flux-tube dynamics in the solar interior

Helicity of solar magnetic field from observations

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