The Effect of Activity-Related Meridional Flow Modulation on the Strength of the Solar Polar Magnetic Field

Jiang, Jingyang; Işık, Emre; Cameron, R. H.; Schmitt, D.; Schüßler, M.

doi:10.1088/0004-637x/717/1/597

Cited by 77 publications

(77 citation statements)

References 33 publications

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“…Sun et al (2015) found an anti-correlation between active region field strength and the mid-latitude poleward flow speed of the associated decayed field, consistent with a fielddependent converging flow towards active regions (Zhao and Kosovichev, 2004). Using a fluxtransport model, Jiang et al (2010) studied the effect of meridional flow perturbations caused by near-surface inflows towards the active region band in each hemisphere, and found that large perturbations reduce the tilt angles of bipoles, thus reducing their contribution to the polar field changes. The amplitude of the meridional flow perturbations are larger for stronger solar cycles, consistent with the anti-correlation between Joy's law tilt and cycle amplitude reported by Dasi-Espuig et al (2010).…”

Section: Unusual Cycle 23 Minimummentioning

confidence: 86%

Solar Magnetism in the Polar Regions

Petrie

2015

Living Rev. Sol. Phys.

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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: 86%

Solar Magnetism in the Polar Regions

Petrie

2015

Living Rev. Sol. Phys.

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“…a stronger cycle produces a smaller tilt angle and therefore a weaker poloidal seed field for the n+1 cycle (Cameron and Schüssler, 2012). Jiang et al (2010) study the effect of meridional flow perturbations and find that larger perturbations reduce the tilt angle of bipolar magnetic regions and thus diminish its contribution to the polar field. The perturbations are caused by near-surface inflows towards the active region band in each hemisphere, and the perturbation amplitude increases with stronger magnetic cycles.…”

Section: Discussionmentioning

confidence: 99%

Recovering Joy’s Law as a Function of Solar Cycle, Hemisphere, and Longitude

McClintock

Norton

2013

Sol Phys

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Bipolar active regions in both hemispheres tend to be tilted with respect to the East -West equator of the Sun in accordance with Joy's law that describes the average tilt angle as a function of latitude. Mt. Wilson observatory data from 1917 -1985 are used to analyze the active-region tilt angle as a function of solar cycle, hemisphere, and longitude, in addition to the more common dependence on latitude. Our main results are as follows: i) We recommend a revision of Joy's law toward a weaker dependence on latitude (slope of 0.13 -0.26) and without forcing the tilt to zero at the Equator. ii) We determine that the hemispheric mean tilt value of active regions varies with each solar cycle, although the noise from a stochastic process dominates and does not allow for a determination of the slope of Joy's law on an 11-year time-scale. iii) The hemispheric difference in mean tilt angles, 1.1° + 0.27, over Cycles 16 to 21 was significant to a three-σ level, with average tilt angles in the northern and southern hemispheres of 4.7° + 0.26 and 3.6° + 0.27 respectively. iv) Area-weighted mean tilt angles normalized by latitude for Cycles 15 to 21 anti-correlate with cycle strength for the southern hemisphere and whole-Sun data, confirming previous results by Dasi-Espuig, Solanki, Krivova, et al. (2010, Astron. Astrophys. 518, A7). The northern hemispheric mean tilt angles do not show a dependence on cycle strength. vi) Mean tilt angles do not show a dependence on longitude for any hemisphere or cycle. In addition, the standard deviation of the mean tilt is 29 -31° for all cycles and hemispheres indicating that the scatter is due to the same consistent process even if the mean tilt angles vary.

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“…At this point the inflows are so weak that the subsequent evolution of the BMR is dominated by the differential rotation and the random walk. It should be noted that inflows restrict the growth of the latitudinal separation of polarities over time rather than reducing it (see Jiang et al 2010). The decrease in B p is a consequence of how the latitudinal separation and the enhanced flux destruction balance.…”

Section: Dependence Upon Initial Tiltmentioning

confidence: 99%

“…They found that, even for comparatively weak inflows, the inflows cause the magnetic concentrations to clump together and generate patterns that are inconsistent with observations. Jiang et al (2010) included a magnetic-field-dependent, axisymmetric latitudinal perturbation of the meridional flow compatible with the inflows in SFT simulations and found that this reduced the latitudinal separation of the polarities of the emerged BMRs, thus limiting the buildup of magnetic field at the polar caps. Cameron & Schüssler (2012) argue that this effect dominates in strong cycles, while in weak cycles the perturbation of the meridional flow enhances crossequatorial flux transport and accelerates the reversal of the polar fields.…”

Section: Introductionmentioning

confidence: 99%

Surface flux transport simulations: Effect of inflows toward active regions and random velocities on the evolution of the Sun’s large-scale magnetic field

Martin-Belda

Cameron

2016

A&A

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Aims. We aim to determine the effect of converging flows on the evolution of a bipolar magnetic region (BMR), and to investigate the role of these inflows in the generation of poloidal flux. We also discuss whether the flux dispersal due to turbulent flows can be described as a diffusion process. Methods. We developed a simple surface flux transport model based on point-like magnetic concentrations. We tracked the tilt angle, the magnetic flux and the axial dipole moment of a BMR in simulations with and without inflows and compared the results. To test the diffusion approximation, simulations of random walk dispersal of magnetic features were compared against the predictions of the diffusion treatment. Results. We confirm the validity of the diffusion approximation to describe flux dispersal on large scales. We find that the inflows enhance flux cancellation, but at the same time affect the latitudinal separation of the polarities of the bipolar region. In most cases the latitudinal separation is limited by the inflows, resulting in a reduction of the axial dipole moment of the BMR. However, when the initial tilt angle of the BMR is small, the inflows produce an increase in latitudinal separation that leads to an increase in the axial dipole moment in spite of the enhanced flux destruction. This can give rise to a tilt of the BMR even when the BMR was originally aligned parallel to the equator.

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The Effect of Activity-Related Meridional Flow Modulation on the Strength of the Solar Polar Magnetic Field

Cited by 77 publications

References 33 publications

Solar Magnetism in the Polar Regions

Solar Magnetism in the Polar Regions

Recovering Joy’s Law as a Function of Solar Cycle, Hemisphere, and Longitude

Surface flux transport simulations: Effect of inflows toward active regions and random velocities on the evolution of the Sun’s large-scale magnetic field

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