A THEORETICAL STUDY OF THE BUILD-UP OF THE SUN’S POLAR MAGNETIC FIELD BY USING A 3D KINEMATIC DYNAMO MODEL

AbstractThe evolution of magnetic field is numerically studied for an isolated magnetar, assuming vacuum exterior. Nonlinear coupling between poloidal and toroidal components of the magnetic field can be seen in the initial Hall-drift timescale. Consequently, the polar field at the surface is highly distorted during the phase. This result is suggestive. Fixed dipole magnetic field has been used so far in the theoretical study of the interaction between magnetosphere and accreting matter. In the accretion to magnetar, time-dependent polar magnetic field should be taken into account.

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The Sun’s polar magnetic field: datasets, proxies and theoretical issues

Proceedings of the International Astronomical Union ◽

10.1017/s1743921318001345 ◽

2018 ◽

Vol 13 (S340) ◽

pp. 289-292

Author(s):

Arnab Rai Choudhuri

Keyword(s):

Magnetic Field ◽

Transport Model ◽

Sunspot Cycle ◽

Surface Flux ◽

Dynamo Model ◽

Flux Transport ◽

Polar Magnetic Field ◽

Theoretical Issues ◽

Dynamo Process ◽

Good Precursor

AbstractThe polar magnetic field of the Sun is a manifestation of certain aspects of the dynamo process and is a good precursor for predicting a sunspot cycle before its onset. Although actual synoptic measurements of this field exist only from the mid-1970s, it has now been possible to determine its evolution from the beginning of the twentieth century with the help of various proxies. The recently developed 3D kinematic dynamo model can study the build-up of the Sun’s polar magnetic field more realistically than the earlier surface flux transport model.

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Solar Internal Rotation and Dynamo Waves: A Two-Dimensional Asymptotic Solution in the Convection Zone

International Astronomical Union Colloquium ◽

10.1017/s0252921100064861 ◽

2000 ◽

Vol 179 ◽

pp. 379-380

Author(s):

Gaetano Belvedere ◽

Kirill Kuzanyan ◽

Dmitry Sokoloff

Keyword(s):

Magnetic Field ◽

Asymptotic Solution ◽

Internal Rotation ◽

Convection Zone ◽

General Idea ◽

Dynamo Model ◽

Axially Symmetric ◽

Dynamo Action ◽

Regeneration Rate ◽

Dynamo Waves

Extended abstractHere we outline how asymptotic models may contribute to the investigation of mean field dynamos applied to the solar convective zone. We calculate here a spatial 2-D structure of the mean magnetic field, adopting real profiles of the solar internal rotation (the Ω-effect) and an extended prescription of the turbulent α-effect. In our model assumptions we do not prescribe any meridional flow that might seriously affect the resulting generated magnetic fields. We do not assume apriori any region or layer as a preferred site for the dynamo action (such as the overshoot zone), but the location of the α- and Ω-effects results in the propagation of dynamo waves deep in the convection zone. We consider an axially symmetric magnetic field dynamo model in a differentially rotating spherical shell. The main assumption, when using asymptotic WKB methods, is that the absolute value of the dynamo number (regeneration rate) |D| is large, i.e., the spatial scale of the solution is small. Following the general idea of an asymptotic solution for dynamo waves (e.g., Kuzanyan & Sokoloff 1995), we search for a solution in the form of a power series with respect to the small parameter |D|–1/3(short wavelength scale). This solution is of the order of magnitude of exp(i|D|1/3S), where S is a scalar function of position.

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Polar Magnetic Field Reversals of the Sun in Maunder Minimum

International Astronomical Union Colloquium ◽

10.1017/s0252921100064472 ◽

2000 ◽

Vol 179 ◽

pp. 193-196

Author(s):

V. I. Makarov ◽

A. G. Tlatov

Keyword(s):

Magnetic Field ◽

Maunder Minimum ◽

The Sun ◽

Annual Rings ◽

Field Reversal ◽

Polar Magnetic Field ◽

Pine Trees ◽

Using Data ◽

Magnetic Field Reversal

AbstractA possible scenario of polar magnetic field reversal of the Sun during the Maunder Minimum (1645–1715) is discussed using data of magnetic field reversals of the Sun for 1880–1991 and the14Ccontent variations in the bi-annual rings of the pine-trees in 1600–1730 yrs.

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An 84-μG Magnetic Field in a Galaxy at Z=0.692?

Proceedings of the International Astronomical Union ◽

10.1017/s1743921308027439 ◽

2008 ◽

Vol 4 (S254) ◽

pp. 95-96

Author(s):

Arthur M. Wolfe ◽

Regina A. Jorgenson ◽

Timothy Robishaw ◽

Carl Heiles ◽

Jason X. Prochaska

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Faraday Rotation ◽

Large Scale ◽

Dynamo Model ◽

Magnetic Field Generation ◽

Interstellar Gas ◽

Splitting Technique ◽

Average Value ◽

The Magnetic Field

AbstractThe magnetic field pervading our Galaxy is a crucial constituent of the interstellar medium: it mediates the dynamics of interstellar clouds, the energy density of cosmic rays, and the formation of stars (Beck 2005). The field associated with ionized interstellar gas has been determined through observations of pulsars in our Galaxy. Radio-frequency measurements of pulse dispersion and the rotation of the plane of linear polarization, i.e., Faraday rotation, yield an average value B ≈ 3 μG (Han et al. 2006). The possible detection of Faraday rotation of linearly polarized photons emitted by high-redshift quasars (Kronberg et al. 2008) suggests similar magnetic fields are present in foreground galaxies with redshifts z > 1. As Faraday rotation alone, however, determines neither the magnitude nor the redshift of the magnetic field, the strength of galactic magnetic fields at redshifts z > 0 remains uncertain.Here we report a measurement of a magnetic field of B ≈ 84 μG in a galaxy at z =0.692, using the same Zeeman-splitting technique that revealed an average value of B = 6 μG in the neutral interstellar gas of our Galaxy (Heiles et al. 2004). This is unexpected, as the leading theory of magnetic field generation, the mean-field dynamo model, predicts large-scale magnetic fields to be weaker in the past, rather than stronger (Parker 1970).The full text of this paper was published in Nature (Wolfe et al. 2008).

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The magnetic helicity density patterns from non-axisymmetric solar dynamo

Journal of Plasma Physics ◽

10.1017/s0022377820001609 ◽

2021 ◽

Vol 87 (1) ◽

Author(s):

Valery V. Pipin

Keyword(s):

Magnetic Field ◽

Differential Rotation ◽

Conservation Law ◽

Large Scale ◽

Solar Dynamo ◽

Magnetic Helicity ◽

Dynamo Model ◽

Density Distributions ◽

Large Scale Magnetic Field ◽

Helicity Conservation

We study the helicity density patterns which can result from the emerging bipolar regions. Using the relevant dynamo model and the magnetic helicity conservation law we find that the helicity density patterns around the bipolar regions depend on the configuration of the ambient large-scale magnetic field, and in general they show a quadrupole distribution. The position of this pattern relative to the equator can depend on the tilt of the bipolar region. We compute the time–latitude diagrams of the helicity density evolution. The longitudinally averaged effect of the bipolar regions shows two bands of sign for the density distributions in each hemisphere. Similar helicity density patterns are provided by the helicity density flux from the emerging bipolar regions subjected to surface differential rotation.

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