Storage of Magnetic Flux in the Overshoot Region

Moreno‐Insertis, F.; Schüßler, M.; Ferriz-Mas, A.

doi:10.1007/978-94-011-0772-3_6

Cited by 80 publications

(132 citation statements)

References 2 publications

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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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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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Section: Introductionmentioning

confidence: 99%

Is there a planetary influence on solar activity?

Abreu

Beer

Ferriz-Mas

et al. 2012

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145

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“…Moreno-Insertis et al (1992) demonstrated that a toroidal flux tube rotating initially at the same rate as the external medium can reach this equilibrium by developing an internal prograde flow. The speed of this "equilibrium" flow depends on the magnetic field strength, depth, and latitude.…”

Section: Friction-induced Instabilitiesmentioning

confidence: 99%

“…Numerical studies simulating a layer of horizontal magnetic field in the bottom of the solar convection zone indicate that an initially uniform field underlying a fieldfree layer leads to the formation of magnetic flux tubes by magnetic Rayleigh-Taylor instability (e.g., Fan 2001). Following its formation, a toroidal magnetic flux tube can reach a mechanical equilibrium close to the bottom of the convection zone (Moreno-Insertis et al 1992). The emergence of magnetic flux tubes driven by magnetic buoyancy and the properties of active regions (low-latitude emergence, tilt angles, proper motions of sunspots) require azimuthal flux densities of the order of 10 5 G in the overshoot region (D'Silva & Choudhuri 1993;Fan et al 1994;Caligari et al 1995;Schüssler 1996).…”

Section: Introductionmentioning

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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“…In the limit of small amplitude, such oscillations occur with the Brunt-Väisälä frequency (in of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0074180900173838 its modified form that incorporates the effect of the magnetic field, non-cartesian geometry, etc, see Moreno-Insertis, Schüssler and Ferriz-Mas (1992). In the same limit, one can easily determine the amplitude of the oscillation of a magnetic ring initially in thermal equilibrium.…”

Section: Non-rotating Case: Vertical Trapping and Poleward Driftmentioning

confidence: 99%

“…Then we discuss the stabilization of the poleward drift of the tube through rotation. A more complete presentation of the following results can be found in Moreno-Insertis, Schüssler and Ferriz-Mas (1992).…”

Section: Introductionmentioning

confidence: 99%

Storage of Magnetic Flux in the Overshoot Region

Moreno‐Insertis

Schüßler

Ferriz-Mas

1993

Symp. - Int. Astron. Union

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A b s t r a c t . The combined action of the subadiabatic ambient stratification in the overshoot region below the convection zone and the inertial forccs associated with the solar rotation is shown to lead to the suppression of the escape of magnetic flux in the form of toroidal flux tubes both toward the surface and toward higher latitudes. We show that a flux ring initially in thermal equilibrium with its environment and rotating with the ambient angular velocity moves radially and latitudinally towards an equilibrium configuration of lower internal temperature and larger internal rotation rate with respect to the surrounding, field-free gas. We conclude that flux rings with B< 10 G can be kept within the overshoot region if the superadiabaticity is sufficiently negative, i.e. δ = V --10"~5; below that field strength the poleward drift is also rcduccd to a latitudinal oscillation of moderate amplitude, AO ^ 20 dcg. Flux rings with significantly larger field strength cannot be kept in the equatorial parts of the overshoot region: their equilibrium configuration is located at high latitudes far outside the solar activity belts and, at any rate, requires unrealistic values of δ.K e y words: Sun: magnetic field -stars: magnetic field -magnetic flux tubes -dynamo

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Storage of Magnetic Flux in the Overshoot Region

Cited by 80 publications

References 2 publications

Is there a planetary influence on solar activity?

Is there a planetary influence on solar activity?

Flow instabilities of magnetic flux tubes

Storage of Magnetic Flux in the Overshoot Region

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