Instabilities of magnetic flux tubes in a stellar convection zone I. Equatorial flux rings in differentially rotating stars

Ferriz-Mas, A.; Schüßler, M.

doi:10.1080/03091929308203613

Cited by 70 publications

(74 citation statements)

References 21 publications

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“…For latitudinal motions out of the equatorial plane, the axisymmetric component is unstable, which corresponds to the poleward slip of the tube as a whole. But this instability can be suppressed when Living Reviews in Solar Physics http://www.livingreviews.org/lrsp-2009-4 the Coriolis force is included (Ferriz-Mas and Schüssler, 1993). For motions within the equatorial plane, the conditions for instabilities are (Spruit and van Ballegooijen, 1982a,b) …”

Section: The Buoyancy Instability Of Isolated Toroidal Magnetic Flux mentioning

confidence: 99%

“…Applying the above assumptions to the ideal MHD momentum equation, Spruit (1981) derived the equation of motion of a thin untwisted magnetic flux tube embedded in a field-free fluid. Taking into account the differential rotation of the Sun, Ω e (r) = Ω e (r)ẑ, the equation of motion for the thin flux tube in a rotating reference frame of angular velocity Ω = Ωẑ is (Ferriz-Mas and Schüssler, 1993;Caligari et al, 1995) …”

Section: Living Reviews In Solar Physicsmentioning

confidence: 99%

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Magnetic Fields in the Solar Convection Zone

Fan

2009

Living Rev. Sol. Phys.

279

263

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Active regions on the solar surface are generally thought to originate from a strong toroidal magnetic field generated by a deep seated solar dynamo mechanism operating at the base of the solar convection zone. Thus the magnetic fields need to traverse the entire convection zone before they reach the photosphere to form the observed solar active regions. Understanding this process of active region flux emergence is therefore a crucial component for the study of the solar cycle dynamo. This article reviews studies with regard to the formation and rise of active region scale magnetic flux tubes in the solar convection zone and their emergence into the solar atmosphere as active regions. The date given as then uniquely identifies the version of the article you are referring to. Article RevisionsLiving Reviews supports two different ways to keep its articles up-to-date:Fast-track revision A fast-track revision provides the author with the opportunity to add short notices of current research results, trends and developments, or important publications to the article. A fast-track revision is refereed by the responsible subject editor. If an article has undergone a fast-track revision, a summary of changes will be listed here.Major update A major update will include substantial changes and additions and is subject to full external refereeing. It is published with a new publication number.

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Section: The Buoyancy Instability Of Isolated Toroidal Magnetic Flux mentioning

confidence: 99%

Section: Living Reviews In Solar Physicsmentioning

confidence: 99%

Magnetic Fields in the Solar Convection Zone

Fan

2009

Living Rev. Sol. Phys.

279

263

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“…Since the idea was first put forward by Galloway & Weiss (1981), many solar physicists believe that the tachocline plays a fundamental role in the generation and storage of the toroidal magnetic flux that eventually gives rise to solar active regions (van Ballegooijen 1982;Charbonneau 2010). The relative position between these two boundary layers -one mechanical and one thermal -determines the degree of subadiabaticity of the tachocline and therefore its capability to store magnetic flux tubes (Moreno-Insertis et al 1992;Ferriz-Mas & Schüssler 1993Fan 2009). The tachocline is also important because tides therein can excite gravity waves (whose restoring force is buoyancy).…”

Section: Introductionmentioning

confidence: 99%

Is there a planetary influence on solar activity?

Abreu

Beer

Ferriz-Mas

et al. 2012

A&A

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145

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Context. Understanding the Sun's magnetic activity is important because of its impact on the Earth's environment. Direct observations of the sunspots since 1610 reveal an irregular activity cycle with an average period of about 11 years, which is modulated on longer timescales. Proxies of solar activity such as 14 C and 10 Be show consistently longer cycles with well-defined periodicities and varying amplitudes. Current models of solar activity assume that the origin and modulation of solar activity lie within the Sun itself; however, correlations between direct solar activity indices and planetary configurations have been reported on many occasions. Since no successful physical mechanism was suggested to explain these correlations, the possible link between planetary motion and solar activity has been largely ignored. Aims. While energy considerations clearly show that the planets cannot be the direct cause of the solar activity, it remains an open question whether the planets can perturb the operation of the solar dynamo. Here we use a 9400 year solar activity reconstruction derived from cosmogenic radionuclides to test this hypothesis. Methods. We developed a simple physical model for describing the time-dependent torque exerted by the planets on a non-spherical tachocline and compared the corresponding power spectrum with that of the reconstructed solar activity record. Results. We find an excellent agreement between the long-term cycles in proxies of solar activity and the periodicities in the planetary torque and also that some periodicities remain phase-locked over 9400 years. Conclusions. Based on these observations we put forward the idea that the long-term solar magnetic activity is modulated by planetary effects. If correct, our hypothesis has important implications for solar physics and the solar-terrestrial connection.

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“…The numerical procedure is based on the equations of ideal magnetohydrodynamics in the framework of the thin flux tube approximation (Spruit 1981), in the form given by Ferriz-Mas & Schüssler (1993. In the numerical scheme, the flux tube is described by a string of Lagrangian mass elements, which move in three dimensions under the effects of various body forces.…”

Section: Nonlinear Simulationsmentioning

confidence: 99%

“…We adopt the linearised equations of thin magnetic flux tubes as given by Ferriz-Mas & Schüssler (1993 and apply the drag force exerted by an azimuthally periodic flow of the form…”

Section: Solution Proceduresmentioning

confidence: 99%

Flow instabilities of magnetic flux tubes

Işık

Holzwarth

2009

A&A

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Context. Flow-induced instabilities of magnetic flux tubes are relevant to the storage of magnetic flux in the interiors of stars with outer convection zones. The stability of magnetic fields in stellar interiors is of importance to the generation and transport of solar and stellar magnetic fields. Aims. We consider the effects of material flows on the dynamics of toroidal magnetic flux tubes located close to the base of the solar convection zone, initially within the overshoot region. The problem is to find the physical conditions in which magnetic flux can be stored for periods comparable to the dynamo amplification time, which is of the order of a few years. Methods. We carry out nonlinear numerical simulations to investigate the stability and dynamics of thin flux tubes subject to perpendicular and longitudinal flows. We compare the simulations with the results of simplified analytical approximations. Results. The longitudinal flow instability induced by the aerodynamic drag force is nonlinear in the sense that the growth rate depends on the perturbation amplitude. This result is consistent with the predictions of linear theory. Numerical simulations without friction show that nonlinear Parker instability can be triggered below the linear threshold of the field strength, when the difference in superadiabaticity along the tube is sufficiently large. A localised downflow acting on a toroidal tube in the overshoot region leads to instability depending on the parameters describing the flow, as well as the magnetic field strength. We determined ranges of the flow parameters for which a linearly Parker-stable magnetic flux tube is stored in the middle of the overshoot region for a period comparable to the dynamo amplification time. Conclusions. The longitudinal flow instability driven by frictional interaction of a flux tube with its surroundings is relevant to determining the storage time of magnetic flux in the solar overshoot region. The residence time for magnetic flux tubes with 2 × 10 21 Mx in the convective overshoot layer can be comparable to the dynamo amplification time, provided that the average speed and the duration of an external downflow do not exceed about 50 m s −1 and 100 days, respectively, and that the lateral extension of the flow is smaller than about 10• .

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Instabilities of magnetic flux tubes in a stellar convection zone I. Equatorial flux rings in differentially rotating stars

Cited by 70 publications

References 21 publications

Magnetic Fields in the Solar Convection Zone

Magnetic Fields in the Solar Convection Zone

Is there a planetary influence on solar activity?

Flow instabilities of magnetic flux tubes

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