Topological pumping of magnetic flux by three-dimensional convection

Drobyshevski, E. M.; Yuferev, V. S.

doi:10.1017/s0022112074001236

Cited by 121 publications

(48 citation statements)

References 6 publications

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“…Unlike the large-scale circulation, γ is not divergenceless. Theoretical analysis and local magneto-convection simulations predict a downward magnetic pumping in the SCZ (Drobyshevski & Yuferev 1974;Krause & Rädler 1980;Petrovay & Szakaly 1993;Tobias et al 1998; Käpylä et al 2009; Karak et al 2014c). The recent rapidly rotating convection simulations in stellar CZs (e.g., Augustson et al 2015;Warnecke et al 2016) also find magnetic pumping, although in some cases, it is radially outward at some latitudes.…”

Section: Modelmentioning

confidence: 99%

Babcock–leighton Solar Dynamo: The Role of Downward Pumping and the Equatorward Propagation of Activity

Karak

Cameron

2016

ApJ

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The key elements of the Babcock-Leighton dynamos are the generation of poloidal field through decay and dispersal of tilted bipolar active regions and the generation of toroidal field through the observed differential rotation. These models are traditionally known as flux transport dynamo models as the equatorward propagations of the butterfly wings in these models are produced due to an equatorward flow at the bottom of the convection zone. Here we investigate the role of downward magnetic pumping near the surface using a kinematic Babcock-Leighton model. We find that the pumping causes the poloidal field to become predominately radial in the near-surface shear layer, which allows the negative radial shear to effectively act on the radial field to produce a toroidal field. We observe a clear equatorward migration of the toroidal field at low latitudes as a consequence of the dynamo wave even when there is no meridional flow in the deep convection zone. Both the dynamo wave and the flux transport type solutions are thus able to reproduce some of the observed features of the solar cycle, including the 11-year periodicity. The main difference between the two types of solutions is the strength of the Babcock-Leighton source required to produce the dynamo action. A second consequence of the magnetic pumping is that it suppresses the diffusion of fields through the surface, which helps to allow an 11-year cycle at (moderately) larger values of magnetic diffusivity than have previously been used.

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Section: Modelmentioning

confidence: 99%

Babcock–leighton Solar Dynamo: The Role of Downward Pumping and the Equatorward Propagation of Activity

Karak

Cameron

2016

ApJ

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“…The existence of magnetic pumping has been known for several decades now. Drobyshevski & Yuferev (1974) demonstrated in a numerical investigation that magnetic flux in a convective layer is expelled downward if the downflows form connected lanes that separate isolated upflowing regions, an effect known as topological pumping (cf. also Moffatt 1978, p. 70;Petrovay 1991).…”

Section: Introductionmentioning

confidence: 99%

Magnetoconvection and dynamo coefficients

Ossendrijver

Stix

Brandenburg

et al. 2002

A&A

107

136

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Abstract.We study the pumping of magnetic flux in three-dimensional compressible magnetoconvection in the context of stellar dynamos. The simulation domain represents a rectangular section from the lower part of a stellar convection zone plus the underlying stably stratified layer, with a total depth of up to five pressure scale heights. Once convection has attained a statistically stationary state, a magnetic field is introduced. The magnetic field is subsequently modified by the convective motions, and the resulting pumping effects are isolated by calculating various coefficients of the expansion of the electromotive force, u × b, in terms of components of the mean magnetic field. The dependence of the pumping effects on rotation, latitude and other parameters is studied. First numerical evidence is found for the existence of pumping effects in the horizontal directions. Evidence is found that the pumping effects act differently on different components of the mean magnetic field. Latitudinal pumping is mainly equatorward for a toroidal field, and can be poleward for a poloidal field. Longitudinal pumping is mainly retrograde for the radial field but prograde for the latitudinal field. The pumping effect in the vertical direction is found to be dominated by the diamagnetic effect, equivalent to a predominating downward advection with a maximum speed in the turbulent case of about 10% of the rms convective velocity. Where possible, an attempt is made to identify the physical origin of the effect. Finally, some consequences of the results for stellar dynamos are discussed.

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“…This can explain only high-latitude filaments, and cannot explain filaments at low latitudes or large quiescent filaments nearly elongated in the meridional direction. Earlier, we briefly discussed in [24] the possibility of forming large-scale horizontal magnetic fields in subphotospheric layers, along the boundaries of supergranules, by a mechanism of topological pumping [26], and the role of supergranulation motions near polarity-inversion lines of the large-scale magnetic field [4]. This mechanism of magnetic-field formation is possible both in a quiet atmosphere and an active region.…”

Section: The Formation Of the Axial Magnetic Field In A Filamentmentioning

confidence: 99%

Evolution of a filament due to magnetic-field variations in a complex active region

2006

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Abstract-The complex active region NOAA 9672 is studied when it was near the central meridian, from October 21-26, 2001. At that time, there was an emergence of new magnetic flux, with the ongoing formation of a filament. The dynamics of the magnetic field are studied in order to search for their possible manifestations in the filament structure, using SOHO MDI magnetograms, SOHO EIT and TRACE filtergrams in the 171Å line, and Hα filtergrams available via the Internet. Our earlier conclusion that filaments form at the boundaries of supergranules near polarity-inversion lines is confirmed. The conclusion of Chae that sinistral filaments have positive magnetic helicity is also confirmed. New information about magnetic-field decay processes is obtained. The direction of motion of the magnetic poles and their relative positions suggest that the axial field of a filament forms as a result of either reconnection of cancelling magnetic poles, or emergence of horizontal magnetic-flux tubes.PACS numbers : 96.60.R

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Topological pumping of magnetic flux by three-dimensional convection

Cited by 121 publications

References 6 publications

Babcock–leighton Solar Dynamo: The Role of Downward Pumping and the Equatorward Propagation of Activity

Babcock–leighton Solar Dynamo: The Role of Downward Pumping and the Equatorward Propagation of Activity

Magnetoconvection and dynamo coefficients

Evolution of a filament due to magnetic-field variations in a complex active region

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