Variations in the Axisymmetric Transport of Magnetic Elements on the Sun: 1996-2010

Hathaway, David H.; Rightmire, Lisa

doi:10.1088/0004-637x/729/2/80

Cited by 87 publications

(104 citation statements)

References 50 publications

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“…The meridional flow speed measurements of Ulrich (2010), Basu and Antia (2010) and Hathaway and Rightmire (2011) do not show evidence of significantly faster flows at active latitudes during cycle 23 than during previous cycles. Moreover, Basu and Antia (2010) concluded that the flow speed variation reported by Hathaway and Rightmire (2010) was associated with a flow pattern that migrated equatorward with the magnetic activity belts.…”

Section: Unusual Cycle 23 Minimummentioning

confidence: 58%

Solar Magnetism in the Polar Regions

Petrie

2015

Living Rev. Sol. Phys.

100

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This review describes observations of the polar magnetic fields, models for the cyclical formation and decay of these fields, and evidence of their great influence in the solar atmosphere. The polar field distribution dominates the global structure of the corona over most of the solar cycle, supplies the bulk of the interplanetary magnetic field via the polar coronal holes, and is believed to provide the seed for the creation of the activity cycle that follows. A broad observational knowledge and theoretical understanding of the polar fields is therefore an essential step towards a global view of solar and heliospheric magnetic fields. Analyses of both high-resolution and long-term synoptic observations of the polar fields are summarized. Models of global flux transport are reviewed, from the initial phenomenological and kinematic models of Babcock and Leighton to present-day attempts to produce time-dependent maps of the surface magnetic field and to explain polar field variations, including the weakness of the cycle 23 polar fields. The relevance of the polar fields to solar physics extends far beyond the surface layers from which the magnetic field measurements usually derive. As well as discussing the polar fields' role in the interior as seed fields for new solar cycles, the review follows their influence outward to the corona and heliosphere. The global coronal magnetic structure is determined by the surface magnetic flux distribution, and is dominated on large scales by the polar fields. We discuss the observed effects of the polar fields on the coronal hole structure, and the solar wind and ejections that travel through the atmosphere. The review concludes by identifying gaps in our knowledge, and by pointing out possible future sources of improved observational information and theoretical understanding of these fields. Article RevisionsLiving Reviews supports two ways of keeping its articles up-to-date:Fast-track revision. A fast-track revision provides the author with the opportunity to add short notices of current research results, trends and developments, or important publications to the article. A fast-track revision is refereed by the responsible subject editor. If an article has undergone a fast-track revision, a summary of changes will be listed here.Major update. A major update will include substantial changes and additions and is subject to full external refereeing. It is published with a new publication number.For detailed documentation of an article's evolution, please refer to the history document of the article's online version at http://dx

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Section: Unusual Cycle 23 Minimummentioning

confidence: 58%

Solar Magnetism in the Polar Regions

Petrie

2015

Living Rev. Sol. Phys.

100

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“…For instance, the results of Hathaway (2010) indicate that the meridional flow speed during the decay phase of cycle 23 was nearly 20% higher than during the corresponding phase in cycle 22. Furthermore, the meridional flow profile used in the flux transport simulation probably underestimates the poleward velocities beyond 60 • latitude (Hathaway and Rightmire 2011). On the other hand, polar countercells of the meridional flow could redistribute flux from the polar cap to lower latitudes and thus also contribute to weaker polar fields (Jiang et al 2009).…”

Section: Resultsmentioning

confidence: 99%

Can Surface Flux Transport Account for the Weak Polar Field in Cycle 23?

et al. 2011

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To reproduce the weak magnetic field on the polar caps of the Sun observed during the declining phase of cycle 23 poses a challenge to surface flux transport models since this cycle has not been particularly weak. We use a well-calibrated model to evaluate the parameter changes required to obtain simulated polar fields and open flux that are consistent with the observations. We find that the low polar field of cycle 23 could be reproduced by an increase of the meridional flow by 55% in the last cycle. Alternatively, a decrease of the mean tilt angle of sunspot groups by 28% would also lead to a similarly low polar field, but cause a delay of the polar field reversals by 1.5 years in comparison to the observations.

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“…We know the value of both Ω| R NSSL and Ω| R from observations. For the surface rotation rate we use the synodic rate for magnetic fields of Hathaway & Rightmire (2011), Ω| R = 14.30 − 1.98 cos 2 θ − 2.14 cos 4 θ [ • /day]. (A.10)…”

Section: Appendix A: Generation Of Toroidal Flux By Differential Rotamentioning

confidence: 99%

The turbulent diffusion of toroidal magnetic flux as inferred from properties of the sunspot butterfly diagram

Cameron

Schüßler

2016

A&A

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Context. In order to match observed properties of the solar cycle, flux-transport dynamo models require the toroidal magnetic flux to be stored in a region of low magnetic diffusivity, typically located at or below the bottom of the convection zone. Aims. We infer the turbulent magnetic diffusivity affecting the toroidal field on the basis of empirical data. Methods. We considered the time evolution of mean latitude and width of the activity belts of solar cycles 12-23 and their dependence on cycle strength. We interpreted the decline phase of the cycles as a diffusion process. Results. The activity level of a given cycle begins to decline when the centers of its equatorward propagating activity belts come within their (full) width (at half maximum) from the equator. This happens earlier for stronger cycles because their activity belts are wider. From that moment on, the activity and the belt width decrease in the same manner for all cycles, independent of their maximum activity level. In terms of diffusive cancellation of opposite-polarity toroidal flux across the equator, we infer the turbulent diffusivity experienced by the toroidal field, wherever it is located, to be in the range 150-450 km 2 s −1 . Strong diffusive latitudinal spreading of the toroidal flux underneath the activity belts can be inhibited by an inflow toward the toroidal field bands in the convection zone with a magnitude of several meters per second. Conclusions. The inferred value of the turbulent magnetic diffusivity affecting the toroidal field agrees, to order of magnitude, with estimates based on mixing-length models for the solar convection zone. This is at variance with the requirement of flux-transport dynamo models. The inflows required to keep the toroidal field bands together before they approach the equator are similar to the inflows toward the activity belts observed with local helioseismology.

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Variations in the Axisymmetric Transport of Magnetic Elements on the Sun: 1996-2010

Cited by 87 publications

References 50 publications

Solar Magnetism in the Polar Regions

Solar Magnetism in the Polar Regions

Can Surface Flux Transport Account for the Weak Polar Field in Cycle 23?

The turbulent diffusion of toroidal magnetic flux as inferred from properties of the sunspot butterfly diagram

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