Mechanisms for magnetic field reversals

Pétrélis, François; Fauve, S.

doi:10.1098/rsta.2009.0250

Cited by 22 publications

(23 citation statements)

References 47 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Field reversals and associated symmetry changes arise also in several related systems, notably the geodynamo (e.g. Roberts and Glatzmaier 2000;Pétrélis et al 2009;Pétrélis & Fauve 2010;Gallet et al 2012) and the VKS experiment, where dynamo action is driven by ferromagnetic rotors in a tank of molten sodium (Ravelet et al 2008;Monchaux et al 2009;Berhanu et al 2010).…”

Section: Introductionmentioning

confidence: 99%

Supermodulation of the Sun's magnetic activity: the effects of symmetry changes

Weiss¹,

Tobias²

2015

Mon. Not. R. Astron. Soc.

View full text Add to dashboard Cite

In this paper we argue that the solar activity record, as revealed by telescopic observations and proxy data from the abundances of cosmogenic isotopes, is consistent with the action of a deterministic nonlinear chaotic dynamo. In particular we claim that the long timescale 'super-modulation' apparent in the isotopic record can be ascribed to switching of the dynamo between two different modulational patterns. The first (which is currently in operation) involves deep grand minima and occasional changes in symmetry triggered by these minima. The second, which exhibits only weak modulation and no grand minima, arises as a consequence of symmetry breaking. These processes are demonstrated for highly idealized simple models of the nonlinear dynamo equations.

show abstract

Section: Introductionmentioning

confidence: 99%

Supermodulation of the Sun's magnetic activity: the effects of symmetry changes

Weiss¹,

Tobias²

2015

Mon. Not. R. Astron. Soc.

View full text Add to dashboard Cite

show abstract

“…In some cases, they can also trigger dynamical reversals between different metastable states, although it has also been reported that, within the experimental observation times, on occasion these fluctuations do not induce such reversals [17]. The search for generic mechanisms for reversals has been initiated and some simple low dimensional models, where for example an unstable mode is coupled to other stable modes, have been proposed [19,20]. It would be interesting to go beyond the quintic subcritical amplitude equation that we propose in this work, searching for such a simple model of interacting modes.…”

Section: Resultsmentioning

confidence: 99%

“…Turbulent flows that present bistability and hysteresis have been studied in the contexts of pure fluid dynamics [10][11][12][13][14][15] and magnetohydrodynamics, particularly concerning the Dynamo instability [16][17][18]. An interesting issue is the possibility of random reversals between two turbulent attractors [10,13,16,19,20]. More generally, the existence of large-scale fields on top of strongly turbulent backgrounds is also present in many geophysical and astrophysical flows.…”

Section: Introductionmentioning

confidence: 99%

Gravity wave instability in a turbulent free-surface Taylor–Couette flow: experiments and comparison with an amplitude equation with additive noise

et al. 2015

View full text Add to dashboard Cite

We present an experimental and theoretical study on the gravity-wave instability developing in a highly turbulent free-surface Taylor-Couette flow, for which only the inner cylinder rotates. Above a critical rotation speed, from an axisymmetric turbulent base state a non-axisymmetric fluctuating gravity-wave state develops, with an m = 1 azimuthal wave number. The bifurcation is discontinuous and presents hysteresis. In contrast to previously reported work (Mujica N and Lathrop D 2006 J. Fluid Mech. 51 49-62), here we compare our experimental results with a universal model based on a quintic subcritical amplitude equation with additive noise. In general, the model describes correctly the mean free-surface oscillation amplitude and its fluctuations, although differences exist in the bistability region width and the free-surface fluctuations in the gravity wave state. These differences are due to the finite time measurements and non-linear effects, respectively. Indeed, we show that longer measurement times allow the system to transit in either direction (from or to the base state), which results in the shrinking of the bistability region. For very long measurement times, and in a very narrow range of rotation rates, the system presents a series of random reversals between both states. Finally, by removing the mean wave and flow oscillations in the measured free-surface and bulk pressure signals, we demonstrate that their dynamic fluctuations depend on the system state.

show abstract

“…Such effects had been neither observed in the Riga nor in the Karlsruhe experiment and thus instigated a strong interest in the geophysics community, with a number of attempts to understand reversals of the geomagnetic field and reversals in the VKS dynamo on the common basis of low-dimensional models [45].…”

Section: Forward Problems: One Examplementioning

confidence: 99%

Forward and inverse problems in fundamental and applied magnetohydrodynamics

Giesecke

Stefani

Wondrak

et al. 2013

Eur. Phys. J. Spec. Top.

View full text Add to dashboard Cite

Abstract. This Minireview summarizes the recent efforts to solve forward and inverse problems as they occur in different branches of fundamental and applied magnetohydrodynamics. As for the forward problem, the main focus is on the numerical treatment of induction processes, including self-excitation of magnetic fields in non-spherical domains and/or under the influence of non-homogeneous material parameters. As an important application of the developed numerical schemes, the functioning of the von-Kármán-sodium (VKS) dynamo experiment is shown to depend crucially on the presence of soft-iron impellers. As for the inverse problem, the main focus is on the mathematical background and some first practical applications of the Contactless Inductive Flow Tomography (CIFT), in which flow induced magnetic field perturbations are utilized for the reconstruction of the velocity field. The promises of CIFT for flow field monitoring in the continuous casting of steel are substantiated by results obtained at a test rig with a low melting liquid metal. While CIFT is presently restricted to flows with low magnetic Reynolds numbers, some selected problems of non-linear inverse dynamo theory, with possible application to geo-and astrophysics, are also discussed.

show abstract

Mechanisms for magnetic field reversals

Cited by 22 publications

References 47 publications

Supermodulation of the Sun's magnetic activity: the effects of symmetry changes

Supermodulation of the Sun's magnetic activity: the effects of symmetry changes

Gravity wave instability in a turbulent free-surface Taylor–Couette flow: experiments and comparison with an amplitude equation with additive noise

Forward and inverse problems in fundamental and applied magnetohydrodynamics

Contact Info

Product

Resources

About