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

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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Optimization of surface flux transport models for the solar polar magnetic field

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936099 ◽

2019 ◽

Vol 632 ◽

pp. A87 ◽

Cited By ~ 6

Author(s):

K. Petrovay ◽

M. Talafha

Keyword(s):

Magnetic Field ◽

Solar Cycle ◽

Parameter Space ◽

Large Scale ◽

Surface Flux ◽

Supporting Evidence ◽

Flux Transport ◽

Polar Magnetic Field ◽

Flow Profiles ◽

Magnetic Diffusivity

Context. The choice of free parameters in surface flux transport (SFT) models describing the evolution of the large-scale poloidal magnetic field of the Sun is critical for the correct reproduction of the polar magnetic flux built up during a solar cycle, which is known to be a good predictor of the amplitude of the upcoming cycle. Aims. For an informed choice of parameters it is important to understand the effects of and interplay among the various parameters and to optimize the models for the polar magnetic field. Methods. Here we present the results of a large-scale systematic study of the parameter space in an SFT model where the source term representing the net effect of tilted flux emergence was chosen to represent a typical, average solar cycle as described by observations. Results. Comparing the results with observational constraints on the spatiotemporal variation of the polar magnetic field, as seen in magnetograms for the last four solar cycles, we mark allowed and excluded regions in the 3D parameter space defined by the flow amplitude u0, the magnetic diffusivity η and the decay time scale τ, for three different assumed meridional flow profiles. Conclusions. Without a significant decay term in the SFT equation (i.e., for τ > 10 yr) the global dipole moment reverses too late in the cycle for all flow profiles and parameters, providing independent supporting evidence for the need of a decay term, even in the case of identical cycles. An allowed domain is found to exist for τ values in the 5–10 yr range for all flow profiles considered. Generally higher values of η (500–800 km2 s−1) are preferred though some solutions with lower η are still allowed.

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

Proceedings of the International Astronomical Union ◽

10.1017/s1743921311015560 ◽

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.

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ON POLAR MAGNETIC FIELD REVERSAL AND SURFACE FLUX TRANSPORT DURING SOLAR CYCLE 24

The Astrophysical Journal ◽

10.1088/0004-637x/798/2/114 ◽

2015 ◽

Vol 798 (2) ◽

pp. 114 ◽

Cited By ~ 72

Author(s):

Xudong Sun ◽

J. Todd Hoeksema ◽

Yang Liu ◽

Junwei Zhao

Keyword(s):

Magnetic Field ◽

Solar Cycle ◽

Surface Flux ◽

Flux Transport ◽

Field Reversal ◽

Polar Magnetic Field ◽

Solar Cycle 24 ◽

Cycle 24 ◽

Magnetic Field Reversal

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Dipolar and Quadrupolar Magnetic Field Evolution over Solar Cycles 21, 22, and 23

Proceedings of the International Astronomical Union ◽

10.1017/s1743921311017492 ◽

2010 ◽

Vol 6 (S271) ◽

pp. 94-101 ◽

Cited By ~ 1

Author(s):

M. L. DeRosa ◽

A. S. Brun ◽

J. T. Hoeksema

Keyword(s):

Magnetic Field ◽

Spherical Harmonic ◽

Transport Model ◽

Activity Cycle ◽

Surface Flux ◽

Solar Activity Cycle ◽

Solar Photosphere ◽

Solar Cycles ◽

Flux Transport ◽

The Past

AbstractTime series of photospheric magnetic field maps from two observatories, along with data from an evolving surface-flux transport model, are decomposed into their constituent spherical harmonic modes. The evolution of these spherical harmonic spectra reflect the modulation of bipole emergence rates through the solar activity cycle, and the subsequent dispersal, shear, and advection of magnetic flux patterns across the solar photosphere. In this article, we discuss the evolution of the dipolar and quadrupolar modes throughout the past three solar cycles (Cycles 21–23), as well as their relation to the reversal of the polar dipole during each solar maximum, and by extension to aspects of the operation of the global solar dynamo.

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The need for active region disconnection in 3D kinematic dynamo simulations

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935986 ◽

2019 ◽

Vol 627 ◽

pp. A168 ◽

Cited By ~ 3

Author(s):

T. Whitbread ◽

A. R. Yeates ◽

A. Muñoz-Jaramillo

Keyword(s):

Solar Cycle ◽

Active Region ◽

Convection Zone ◽

Transport Model ◽

Active Regions ◽

Surface Flux ◽

Dynamo Model ◽

Flux Transport ◽

Kinematic Dynamo ◽

The Difference

In this paper we address a discrepancy between the surface flux evolution in a 3D kinematic dynamo model and a 2D surface flux transport model that has been closely calibrated to the real Sun. We demonstrate that the difference is due to the connectivity of active regions to the toroidal field at the base of the convection zone, which is not accounted for in the surface-only model. Initially, we consider the decay of a single active region, firstly in a simplified Cartesian 2D model and subsequently the full 3D model. By varying the turbulent diffusivity profile in the convection zone, we find that increasing the diffusivity – so that active regions are more rapidly disconnected from the base of the convection zone – improves the evolution of the surface field. However, if we simulate a full solar cycle, we find that the dynamo is unable to sustain itself under such an enhanced diffusivity. This suggests that in order to accurately model the solar cycle, we must find an alternative way to disconnect emerging active regions, whilst conserving magnetic flux.

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Hemispheric injection of magnetic helicity by surface flux transport

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936475 ◽

2019 ◽

Vol 631 ◽

pp. A138 ◽

Cited By ~ 3

Author(s):

G. Hawkes ◽

A. R. Yeates

Keyword(s):

Magnetic Field ◽

Solar Cycle ◽

Solar Rotation ◽

Surface Flux ◽

Magnetic Helicity ◽

Solar Cycles ◽

Flux Transport ◽

Transport Models ◽

Radial Magnetic Field ◽

Helicity Injection

Aims. We estimate the injection of relative magnetic helicity into the solar atmosphere by surface flux transport over 27 solar cycles (1700–2009). Methods. We determine the radial magnetic field evolution using two separate surface flux transport models: one driven by magnetogram inputs and another by statistical active region insertion guided by the sunspot number record. The injection of relative magnetic helicity is then computed from this radial magnetic field together with the known electric field in the flux transport models. Results. Neglecting flux emergence, solar rotation is the dominant contributor to the helicity injection. At high latitudes, the injection is always negative/positive in the northern/southern hemisphere, while at low latitudes the injection tends to have the opposite sign when integrated over the full solar cycle. The overall helicity injection in a given solar cycle depends on the balance between these two contributions. This net injected helicity correlates well with the end-of-cycle axial dipole moment.

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A Three dimensional Babcock-Leighton Solar Dynamo Model with Non-axisymmetric Convective Flows

Proceedings of the International Astronomical Union ◽

10.1017/s1743921318001448 ◽

2018 ◽

Vol 13 (S340) ◽

pp. 301-302

Author(s):

Gopal Hazra ◽

Mark S. Miesch

Keyword(s):

Large Scale ◽

Three Dimensional ◽

Surface Flux ◽

Dynamo Model ◽

Turbulent Diffusivity ◽

Flux Transport ◽

Convective Flows ◽

Solar Observations ◽

Mean Fields ◽

And Migration

AbstractThe observed convective flows on the photosphere (e.g., supergranulation, granulation) play a key role in the Babcock-Leighton (BL) process to generate large scale polar fields from sunspots fields. In most surface flux transport (SFT) and BL dynamo models, the dispersal and migration of surface fields is modeled as an effective turbulent diffusion. We present the first kinematic 3D FT/BL model to explicitly incorporate realistic convective flows based on solar observations. The results obtained are generally in good agreement with the observed surface flux evolution and with non-convective models that have a turbulent diffusivity on the order of 3 × 1012 cm2 s−1 (300 km2 s−1). However, we find that the use of a turbulent diffusivity underestimates the dynamo efficiency, producing weaker mean fields and shorter cycle.

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Modelling short-term Solar Spectral Irradiance (SSI) using coronal electron density and temperature profiles based on solar magnetic field observations

Proceedings of the International Astronomical Union ◽

10.1017/s174392131700182x ◽

2016 ◽

Vol 12 (S327) ◽

pp. 82-85 ◽

Cited By ~ 1

Author(s):

J. M. Rodríguez Gómez ◽

L. E. Antunes Vieira ◽

A. Dal Lago ◽

J. Palacios ◽

L. A. Balmaceda ◽

...

Keyword(s):

Magnetic Field ◽

Solar Magnetic Field ◽

Transport Model ◽

Spectral Irradiance ◽

Source Surface ◽

Solar Cycles ◽

Short Term ◽

Flux Transport ◽

Field Source ◽

Solar Spectral Irradiance

AbstractSome key physical processes that impact the evolution of Earth's atmosphere on time-scale from days to millennia, such as the EUV emissions, are determined by the solar magnetic field. However, observations of the solar spectral irradiance are restricted to the last few solar cycles and are subject to large uncertainties. We present a physics-based model to reconstruct short-term solar spectral irradiance (SSI) variability. The coronal magnetic field is estimated to employ the Potential Field Source Surface extrapolation (PFSS) based on observational synoptic charts and magnetic flux transport model. The emission is estimated to employ the CHIANTI atomic database 8.0. The performance of the model is compared to the emission observed by TIMED/SORCE.

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