The Large-scale Coronal Structure of the 2017 August 21 Great American Eclipse: An Assessment of Solar Surface Flux Transport Model Enabled Predictions and Observations

AbstractStackplot displays of the photospheric magnetic field show long-lived patterns that often rotate at rates differing from the intrinsic photospheric rate. These complex patterns are produced naturally by the flux-transport model, in which magnetic flux emerging in the form of active regions is dispersed over the solar surface by differential rotation, supergranular diffusion, and a poleward meridional flow. Numerical simulations show that long-lived patterns with slopes similar to the observed ones arise even when the longitudes of the erupting flux are randomized, suggesting that a deep-seated longitudinal organization is not required to explain the qualitative nature of the patterns. Both autocorrelation analysis and visual comparison between the slopes of the observed and simulated patterns indicate that the equatorial rotation period of the Sun is close to 26.75 days, significantly shorter than the traditional 26.9 day value of Snodgrass and Newton & Nunn but in agreement with the recent measurements of Komm, Howard, & Harvey. A complete discussion of these results may be found in Sheeley, Wang, & Nash, ApJ, 401, 378 (1992).

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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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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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PREDICTING THE SUN'S POLAR MAGNETIC FIELDS WITH A SURFACE FLUX TRANSPORT MODEL

The Astrophysical Journal ◽

10.1088/0004-637x/780/1/5 ◽

2013 ◽

Vol 780 (1) ◽

pp. 5 ◽

Cited By ~ 78

Author(s):

Lisa Upton ◽

David H. Hathaway

Keyword(s):

Magnetic Fields ◽

Transport Model ◽

Surface Flux ◽

Flux Transport ◽

Polar Magnetic Fields

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How Good Is the Bipolar Approximation of Active Regions for Surface Flux Transport?

Solar Physics ◽

10.1007/s11207-020-01688-y ◽

2020 ◽

Vol 295 (9) ◽

Cited By ~ 1

Author(s):

Anthony R. Yeates

Keyword(s):

Dipole Moment ◽

Active Region ◽

Transport Model ◽

Active Regions ◽

Surface Flux ◽

Flux Transport ◽

Transport Models ◽

Magnetic Structures ◽

Axial Dipole ◽

Flow Parameters

Abstract We investigate how representing active regions with bipolar magnetic regions (BMRs) affects the end-of-cycle polar field predicted by the surface flux transport model. Our study is based on a new database of BMRs derived from the SDO/HMI active region patch data between 2010 and 2020. An automated code is developed for fitting each active region patch with a BMR, matching both the magnetic flux and axial dipole moment of the region and removing repeat observations of the same region. By comparing the predicted evolution of each of the 1090 BMRs with the predicted evolution of their original active region patches, we show that the bipolar approximation leads to a 24% overestimate of the net axial dipole moment, given the same flow parameters. This is caused by neglecting the more complex multipolar and/or asymmetric magnetic structures of many of the real active regions, and may explain why previous flux transport models had to reduce BMR tilt angles to obtain realistic polar fields. Our BMR database and the Python code to extract it are freely available.

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Power spectra of solar brightness variations at various inclinations

Astronomy and Astrophysics ◽

10.1051/0004-6361/202037588 ◽

2020 ◽

Vol 636 ◽

pp. A43 ◽

Cited By ~ 2

Author(s):

N.-E. Nèmec ◽

A. I. Shapiro ◽

N. A. Krivova ◽

S. K. Solanki ◽

R. V. Tagirov ◽

...

Keyword(s):

Transport Model ◽

Solar Rotation ◽

Power Spectra ◽

Surface Flux ◽

The Sun ◽

Space Telescopes ◽

Flux Transport ◽

Total Irradiance ◽

Solar Brightness ◽

Magnetic Features

Context. Magnetic features on the surfaces of cool stars lead to variations in their brightness. Such variations on the surface of the Sun have been studied extensively. Recent planet-hunting space telescopes have made it possible to measure brightness variations in hundred thousands of other stars. The new data may undermine the validity of setting the sun as a typical example of a variable star. Putting solar variability into the stellar context suffers, however, from a bias resulting from solar observations being carried out from its near-equatorial plane, whereas stars are generally observed at all possible inclinations. Aims. We model solar brightness variations at timescales from days to years as they would be observed at different inclinations. In particular, we consider the effect of the inclination on the power spectrum of solar brightness variations. The variations are calculated in several passbands that are routinely used for stellar measurements. Methods. We employ the surface flux transport model to simulate the time-dependent spatial distribution of magnetic features on both the near and far sides of the Sun. This distribution is then used to calculate solar brightness variations following the Spectral And Total Irradiance REconstruction approach. Results. We have quantified the effect of the inclination on solar brightness variability at timescales down to a single day. Thus, our results allow for solar brightness records to be made directly comparable to those obtained by planet-hunting space telescopes. Furthermore, we decompose solar brightness variations into components originating from the solar rotation and from the evolution of magnetic features.

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Connecting measurements of solar and stellar brightness variations

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038054 ◽

2020 ◽

Vol 638 ◽

pp. A56

Author(s):

N.-E. Nèmec ◽

E. Işık ◽

A. I. Shapiro ◽

S. K. Solanki ◽

N. A. Krivova ◽

...

Keyword(s):

Transport Model ◽

Rotation Axis ◽

Surface Flux ◽

Light Curves ◽

The Sun ◽

Solar Cycles ◽

Stellar Rotation ◽

Flux Transport ◽

Surface Distribution ◽

The Difference

Context. A comparison of solar and stellar brightness variations is hampered by the difference in spectral passbands that are used in observations, and also by the possible difference in the inclination of the solar and stellar rotation axes from the line of sight. Aims. We calculate the rotational variability of the Sun as it would be measured in passbands used for stellar observations. In particular, we consider the filter systems used by the CoRoT, Kepler, TESS, and Gaia space missions. We also quantify the effect of the inclination of the rotation axis on the solar rotational variability. Methods. We employed the spectral and total irradiance reconstruction (SATIRE) model to calculate solar brightness variations in different filter systems as observed from the ecliptic plane. We then combined the simulations of the surface distribution of the magnetic features at different inclinations using a surface flux transport model with the SATIRE calculations to compute the dependence of the variability on the inclination. Results. For an ecliptic-bound observer, the amplitude of the solar rotational variability, as observed in the total solar irradiance (TSI), is 0.68 mmag (averaged over solar cycles 21–24). We obtained corresponding amplitudes in the Kepler (0.74 mmag), CoRoT (0.73 mmag), TESS (0.62 mmag), Gaia G (0.74 mmag), Gaia GRP (0.62 mmag), and Gaia GBP (0.86 mmag) passbands. Decreasing the inclination of the rotation axis decreases the rotational variability. For a sample of randomly inclined stars, the variability is on average 15% lower in all filter systems we considered. This almost compensates for the difference in amplitudes of the variability in TSI and Kepler passbands, making the amplitudes derived from the TSI records an ideal representation of the solar rotational variability for comparison to Kepler stars with unknown inclinations. Conclusions. The TSI appears to be a relatively good measure of solar variability for comparisons with stellar measurements in the CoRoT, Kepler, TESS Gaia G, and Gaia GRP filters. Whereas the correction factors can be used to convert the variability amplitude from solar measurements into the values expected for stellar missions, the inclination affects the shapes of the light curves so that a much more sophisticated correction than simple scaling is needed to obtain light curves out of the ecliptic for the Sun.

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Magnetic solar surface flux transport simulation

Iraqi Journal of Physics (IJP) ◽

10.30723/ijp.v13i28.241 ◽

2019 ◽

Vol 13 (28) ◽

pp. 33-43

Author(s):

Loay K. Abood

Keyword(s):

Magnetic Flux ◽

Flux Distribution ◽

Solar Surface ◽

Surface Flux ◽

Surface Velocity ◽

Advection Equation ◽

Implicit Methods ◽

Flux Transport ◽

Tilted Angle ◽

Angle Parameter

In this paper, the solar surface magnetic flux transport has been simulated by solving the diffusion–advection equation utilizing numerical explicit and implicit methods in 2Dsurface. The simulation was used to study the effect of bipolar tilted angle on the solar flux distribution with time. The results show that the tilted angle controls the magnetic distribution location on the sun’s surface, especially if we know that the sun’s surface velocity distribution is a dependent location. Therefore, the tilted angle parameter has distribution influence.

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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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