Emerging Flux Tubes in the Solar Convection Zone. II. The Influence of Initial Conditions

Caligari, P.; Schüßler, M.; Moreno‐Insertis, F.

doi:10.1086/305875

Cited by 89 publications

(97 citation statements)

References 21 publications

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“…They found from their thin flux tube simulations that active region tilts could be explained by Coriolis forces acting on rising, expanding magnetic flux loops, and that if the field strength at the base of the solar convection zone was ∼ 10 5 G, that Joy's law could be reproduced. Similar tilt angle results were also reported by Fan, Fisher, and McClymont (1994), Schüssler et al (1994), Caligari, Moreno-Insertis, and Schüssler (1995), and . These studies employed a wide variety of different initial conditions for the rising loop calculations, but they were all able to reproduce Joy's law for physically reasonable values of the field strength at the base of the convection zone.…”

Section: Joy's Law and Active Region Tiltssupporting

confidence: 89%

“…The theoretical d dependence derived from two effects: tubes with larger magnetic flux (and hence larger d) rise faster and are perturbed less by turbulence, and the larger footpoint separation averages over more distortions in the tube's axis. Values of B which seemed consistent with the observed behavior were in the range (2-4)×10 4 G. The flux tubes in this study were not initially in force balance, and thus the criticisms of Caligari, MorenoInsertis, and and Caligari, Schüssler, and Moreno-Insertis (1998) apply. It is not clear at this time how this might change the field strength that results from a best fit to the observations.…”

Section: Tilt Angle Dispersionsupporting

confidence: 81%

“…Fisher, Fan, and Howard (1995) argued that the best fit to the data from flux tube simulations is obtained for B ≈ (2−3)×10 4 G, based on the simulations of Fan, Fisher, and McClymont (1994). On the other hand, those simulations had initial conditions which were not consistent with flux tubes initially in force balance, as Caligari, Moreno-Insertis, and Schüssler (1995) and Caligari, Schüssler, and Moreno-Insertis (1998) have noted. The simulations assume a more physically self-consistent de-stabilization of the flux tubes.…”

Section: Joy's Law and Active Region Tiltsmentioning

confidence: 95%

“…At the time these simulations were done, dynamo theorists predicted that the field strength near the base of the convection could be no greater than 10 4 G, based on arguments of equipartition between magnetic energy and the kinetic energy density associated with convective motions. Studies of the latitude of active region emergence were also done by Fan, Fisher, and DeLuca (1993), Fan, Fisher, and McClymont (1994), Schüssler et al (1994), Caligari, Moreno-Insertis, and Schüssler (1995), , and Caligari, Schüssler and Moreno-Insertis (1998). Fan, Fisher, and DeLuca (1993), and Fan, Fisher, and McClymont (1994) basically confirmed the results of Choudhuri (1989), namely that if the field strength B 0 is close to the equipartition value (B 0 ∼ 10 4 G), flux emergence occurs at very high latitudes.…”

Section: Latitudes Of Active Region Emergencementioning

confidence: 99%

“…These studies employed a wide variety of different initial conditions for the rising loop calculations, but they were all able to reproduce Joy's law for physically reasonable values of the field strength at the base of the convection zone. Caligari, Schüssler, and Moreno-Insertis (1998) note that active region tilt angles are one of the most robust predictions of thin flux tube models, with tilts depending primarily on latitude and the field strength at the base of the convection zone and not on the details of the initial conditions used in the simulations. Schüssler et al (1994) find best agreement with observed tilts for flux loops originating in the lower part of the convective overshoot region, corresponding to field strengths of (1.2-1.4) × 10 5 G, if the flux loops originate from unstable equilibria.…”

Section: Joy's Law and Active Region Tiltsmentioning

confidence: 99%

See 4 more Smart Citations

The Solar Dynamo and Emerging Flux (Invited Review)

Fisher¹,

Fan²,

Longcope³

et al. 2000

Helioseismic Diagnostics of Solar Convection and Activity

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Abstract. The largest concentrations of magnetic flux on the Sun occur in active regions. In this paper, the properties of active regions are investigated in terms of the dynamics of magnetic flux tubes which emerge from the base of the solar convection zone, where the solar cycle dynamo is believed to operate, to the photosphere. Flux tube dynamics are computed using the 'thin flux tube' approximation, and by using MHD simulation. Simulations of active region emergence and evolution, when compared with the known observed properties of active regions, have yielded the following results:(1) The magnetic field at the base of the convection zone is confined to an approximately toroidal geometry with a field strength in the range (3-10) × 10 4 G. The latitude distribution of the toroidal field at the base of the convection zone is more or less mirrored by the observed active latitudes; there is not a large poleward drift of active regions as they emerge. The time scale for emergence of an active region from the base of the convection zone to the surface is typically 2 -4 months. The equatorial gap in the distribution of active regions has two possible origins; if the toroidal field strength is close to 10 5 G, it is due to the lack of equilibrium solutions at low latitude; if it is closer to 3 × 10 4 G, it may be due to modest poleward drift during emergence. (2) The tilt of active regions is due primarily to the Coriolis force acting to twist the diverging flows of the rising flux loops. The dispersion in tilts is caused primarily by the buffeting of flux tubes by convective motions as they rise through the interior. (3) The Coriolis force also bends the active region flux tube shape toward the following (i.e., anti-rotational) direction, resulting in a steeper leg on the following side as compared to the leading side of an active region. When the active region emerges through the photosphere, this results in a more rapid separation of the leading spots away from the magnetic neutral line as compared to the following spots. This bending motion also results in the neutral line being closer to the following magnetic polarity. (4) Active regions behave kinematically after they emerge because of 'dynamic disconnection', which occurs because of the lack of a solution to the hydrostatic equilibrium equation once the flux loop has emerged. This could explain why active regions decay once they have emerged, and why the advection-diffusion description of active regions works well after emergence. Smaller flux tubes may undergo 'flux tube explosion', a similar process, and provide a source for the constant emergence of small-scale magnetic fields. positive twist in the south can be accounted for by the action of Coriolis forces on convective eddies, which ultimately writhes active region flux tubes to produce a magnetic twist of the correct sign and amplitude to explain the observations. (6) The properties of the strongly sheared, flare productive δ-spot active regions can be accounted for by the dynamics of highly twisted ...

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Section: Joy's Law and Active Region Tiltssupporting

confidence: 89%

Section: Tilt Angle Dispersionsupporting

confidence: 81%

Section: Joy's Law and Active Region Tiltsmentioning

confidence: 95%

Section: Latitudes Of Active Region Emergencementioning

confidence: 99%

Section: Joy's Law and Active Region Tiltsmentioning

confidence: 99%

See 3 more Smart Citations

The Solar Dynamo and Emerging Flux (Invited Review)

Fisher¹,

Fan²,

Longcope³

et al. 2000

Helioseismic Diagnostics of Solar Convection and Activity

View full text Add to dashboard Cite

show abstract

Spot signatures of a solar‐type dynamo in close binary stars

Holzwarth

2004

Astron Nachr

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Abstract. Magnetic activity signatures in the atmosphere of active stars can be used to place constrains on the underlying processes of flux transport and dynamo operation in its convective envelope. The 'solar paradigm' for magnetic activity suggests that the magnetic field is amplified and stored at the base of the convection zone. Once a critical field strength is exceeded, perturbations initiate the onset of instabilities and the growth of magnetic flux loops, which rise through the convection zone, emerge at the stellar surface, and eventually lead to the formation of starspots and active regions. In close binaries, the proximity of the companion star breaks the rotational symmetry. Although the magnitude of tidal distortions is rather small, non-linear MHD simulations have nevertheless shown in the case of main-sequence binary components that they can cause non-uniform surface distributions of flux tube eruptions. The present work extends the investigation to post-mainsequence components to explore the specific influence of the stellar structure on the surface pattern of erupting flux tubes. In contrast to the case of main-sequence components, where the consistency between simulation results and observations supports the presumption of a solar-like dynamo mechanism, the numerical results here do not recover the starspot properties frequently observed on evolved binary components. This aspect points out an insufficiency of the applied flux tube model and leads to the conclusion that additional flux transport and possibly amplification mechanisms have to be taken into account.

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Advection‐dominated solar dynamo model with two‐cell meridional flow and a positive α ‐effect in the tachocline

Bonanno¹,

Elstner

Belvedère

2006

Astron Nachr

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Most probably the sunspot cycle period is ruled by a meridional flow located near the base of the convection zone (Hathaway et al. 2003). On the other hand, if the eddy diffusivity is low enough, dramatic modification of the standard α 2 Ω-dynamo by the meridional flow are expected. In this paper we shall discuss the dependence of periods, dynamo numbers and the sign of the current helicity as a function of the magnetic Reynolds number for a double cell meridional circulation and for a positive α-effect at the base of the convection zone. The dynamo action occurs at lower latitudes and its location is at the interface between equatorward and poleward motions near the base of the convection zone. In spite of the complexity of the flow pattern, our simulations show that the resulting dynamo action reproduces several observed features of the solar cycle.

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Emerging Flux Tubes in the Solar Convection Zone. II. The Influence of Initial Conditions

Cited by 89 publications

References 21 publications

The Solar Dynamo and Emerging Flux (Invited Review)

The Solar Dynamo and Emerging Flux (Invited Review)

Spot signatures of a solar‐type dynamo in close binary stars

Advection‐dominated solar dynamo model with two‐cell meridional flow and a positive α ‐effect in the tachocline

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