Meridional flow in the Sun’s convection zone is a single cell in each hemisphere

Science ◽  
2020 ◽  
Vol 368 (6498) ◽  
pp. 1469-1472 ◽  
Author(s):  
Laurent Gizon ◽  
Robert H. Cameron ◽  
Majid Pourabdian ◽  
Zhi-Chao Liang ◽  
Damien Fournier ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Single Cell ◽  
Convection Zone ◽  
Solar Surface ◽  
Meridional Flow ◽  
Data Sources ◽  
Dynamo Model ◽  
Solar Cycles ◽  
Flux Transport ◽  
The Magnetic Field

The Sun’s magnetic field is generated by subsurface motions of the convecting plasma. The latitude at which the magnetic field emerges through the solar surface (as sunspots) drifts toward the equator over the course of the 11-year solar cycle. We use helioseismology to infer the meridional flow (in the latitudinal and radial directions) over two solar cycles covering 1996–2019. Two data sources are used, which agree during their overlap period of 2001–2011. The time-averaged meridional flow is shown to be a single cell in each hemisphere, carrying plasma toward the equator at the base of the convection zone with a speed of ~4 meters per second at 45° latitude. Our results support the flux-transport dynamo model, which explains the drift of sunspot-emergence latitudes through the meridional flow.

scholarly journals Origin of solar magnetism

2010 ◽  
Vol 6 (S273) ◽  
pp. 28-36 ◽  
Author(s):  
Arnab Rai Choudhuri
Keyword(s):  
Solar Cycle ◽  
Differential Rotation ◽  
Convection Zone ◽  
Meridional Circulation ◽  
Solar Surface ◽  
Dynamo Model ◽  
Solar Cycles ◽  
Poloidal Field ◽  
Flux Transport ◽  
Solar Magnetism

AbstractThe most promising model for explaining the origin of solar magnetism is the flux transport dynamo model, in which the toroidal field is produced by differential rotation in the tachocline, the poloidal field is produced by the Babcock–Leighton mechanism at the solar surface and the meridional circulation plays a crucial role. After discussing how this model explains the regular periodic features of the solar cycle, we come to the questions of what causes irregularities of solar cycles and whether we can predict future cycles. Only if the diffusivity within the convection zone is sufficiently high, the polar field at the sunspot minimum is correlated with strength of the next cycle. This is in conformity with the limited available observational data.

scholarly journals A theoretical model of torsional oscillations from a flux transport dynamo model

2010 ◽  
Vol 6 (S273) ◽  
pp. 366-368
Author(s):  
Piyali Chatterjee ◽  
Sagar Chakraborty ◽  
Arnab Rai Choudhuri
Keyword(s):  
Magnetic Field ◽  
Theoretical Model ◽  
Lorentz Force ◽  
High Latitude ◽  
Torsional Oscillation ◽  
Sunspot Cycle ◽  
Dynamo Model ◽  
Flux Transport ◽  
Torsional Oscillations ◽  
The Magnetic Field

AbstractAssuming that the torsional oscillation is driven by the Lorentz force of the magnetic field associated with the sunspot cycle, we use a flux transport dynamo to model it and explain its initiation at a high latitude before the beginning of the sunspot cycle.

scholarly journals Mean-Field Magnetohydrodynamics of the Solar Convection Zone

1976 ◽  
Vol 71 ◽  
pp. 305-321
Author(s):  
F. Krause
Keyword(s):  
Magnetic Field ◽  
Velocity Field ◽  
Convection Zone ◽  
Solar Surface ◽  
Mean Field ◽  
Solar Convection Zone ◽  
Solar Convection ◽  
Random Character ◽  
Physical Quantities ◽  
The Magnetic Field

Observations of the solar surface show that some of the physical quantities, especially the velocity field and the magnetic field, show random character.

A Dynamo Model for Magnetic Stars with Long Periods

1976 ◽  
Vol 32 ◽  
pp. 39-42
Author(s):  
M. Schüssler
Keyword(s):  
Magnetic Field ◽  
Main Sequence ◽  
Convection Zone ◽  
Dynamo Model ◽  
Magnetic Stars ◽  
Order Of Magnitude ◽  
Linear Effects ◽  
The Right ◽  
Right Order ◽  
The Magnetic Field

SummaryA α - effect dynamo model is presented which can be relevant for the group of magnetic stars.with observed periods between 1 y and 72 ys. The model is based on an axisymmetric α2- dynamo including non-linear effects due to the “cut off α- effect”; no differential rotation is taken into account. There are oscilliations of the magnetic field with periods in the right order of magnitude under the assumption of an outer convection zone between R ≥ r ≥.5 R ….7R. In the sense of this model therefore these stars should be young objects passing from their Hayashi track down to the main sequence.

Probing solar-cycle variations of magnetic fields in the convection zone using meridional flows

2019 ◽  
Vol 15 (S354) ◽  
pp. 160-165
Author(s):  
Chia-Hsien Lin ◽  
Dean-Yi Chou
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Convection Zone ◽  
Deep Convection ◽  
Meridional Flow ◽  
Meridional Plane ◽  
Solar Magnetic Fields ◽  
Magnetic Field Effects ◽  
Astrophysical Journal ◽  
The Magnetic Field

AbstractSolar magnetic fields are believed to originate from the base of convection zone. However, it has been difficult to obtain convincing observational evidence of the magnetic fields in the deep convection zone. The goal of this study is to investigate whether solar meridional flows can be used to detect the magnetic-field effects. Meridional flows are axisymmetric flows on the meridional plane. Our result shows that the flow pattern in the entire convection zone changes significantly from solar minimum to maximum. The changes all centered around active latitudes, suggesting that the magnetic fields are responsible for the changes. The results indicate that the meridional flow can be used to detect the effects of magnetic field in the deep convection zone.The results have been published in the Astrophysical Journal (lc2018).

scholarly journals Small Magnetostatic Flux Tubes

1977 ◽  
Vol 4 (2) ◽  
pp. 265-266
Author(s):  
H. C. Spruit
Keyword(s):  
Magnetic Field ◽  
Heat Transport ◽  
Convective Heat ◽  
Convection Zone ◽  
Solar Surface ◽  
Small Scale ◽  
Flux Tubes ◽  
Basic Assumptions ◽  
Magnetic Elements ◽  
The Magnetic Field

In an attempt to interpret the observed properties of small scale magnetic fields at the solar surface, a set of models has been calculated based on the assumption of a magnetostatic equilibrium. The basic assumptions made are: i.The observed magnetic elements are magnetostatic flux tubes.ii.The efficiency of convective heat transport inside the tube is reduced with respect to that in the normal convection zone; the horizontal convective heat transport in the tube is suppressed completely by the magnetic field.iii.Close to the tube, horizontal convective heat transport is reduced due to the proximity of the magnetic field.

Evolution of Large-Scale Coronal Structures

1994 ◽  
Vol 144 ◽  
pp. 29-33
Author(s):  
P. Ambrož
Keyword(s):  
Magnetic Field ◽  
Field Line ◽  
Large Scale ◽  
Coronal Magnetic Field ◽  
Source Surface ◽  
Solar Cycles ◽  
Characteristic Relationship ◽  
The Magnetic Field ◽  
Coronal Structures

AbstractThe large-scale coronal structures observed during the sporadically visible solar eclipses were compared with the numerically extrapolated field-line structures of coronal magnetic field. A characteristic relationship between the observed structures of coronal plasma and the magnetic field line configurations was determined. The long-term evolution of large scale coronal structures inferred from photospheric magnetic observations in the course of 11- and 22-year solar cycles is described.Some known parameters, such as the source surface radius, or coronal rotation rate are discussed and actually interpreted. A relation between the large-scale photospheric magnetic field evolution and the coronal structure rearrangement is demonstrated.

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

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.

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

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).

Connecting a Star’s Convection Zone with its Corona

1995 ◽  
Vol 12 (2) ◽  
pp. 180-185 ◽  
Author(s):  
D. J. Galloway ◽  
C. A. Jones
Keyword(s):  
Magnetic Field ◽  
Convection Zone ◽  
Flux Rope ◽  
Field System ◽  
Stellar Convection ◽  
Coronal Activity ◽  
Flux Concentration ◽  
Global Understanding ◽  
The Magnetic Field

AbstractThis paper discusses problems which have as their uniting theme the need to understand the coupling between a stellar convection zone and a magnetically dominated corona above it. Interest is concentrated on how the convection drives the atmosphere above, loading it with the currents that give rise to flares and other forms of coronal activity. The role of boundary conditions appears to be crucial, suggesting that a global understanding of the magnetic field system is necessary to explain what is observed in the corona. Calculations are presented which suggest that currents flowing up a flux rope return not in the immediate vicinity of the rope but rather in an alternative flux concentration located some distance away.

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