Loss of toroidal magnetic flux by emergence of bipolar magnetic regions

Cameron, R. H.; Schüßler, M.

doi:10.1051/0004-6361/201937281

Cited by 12 publications

(11 citation statements)

References 29 publications

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“…In summary, this paper deals with the distribution of spots within a sunspot group, providing constraints on the flux emergence processes. In Babcock-Leighton dynamo models, flux emergence plays a key role as it is responsible for both toroidal magnetic flux through the photosphere (Cameron & Schüssler 2020) and for the generation of new poloidal magnetic flux through Joy's law (Hale et al 1919). Despite its critical role, the details of the emergence process remain poorly understood.…”

Section: Discussionmentioning

confidence: 99%

On the size distribution of spots within sunspot groups

Mandal

Krivova

Cameron

et al. 2021

A&A

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The size distribution of sunspots provides key information about the generation and emergence processes of the solar magnetic field. Previous studies of size distribution have primarily focused on either the whole group or individual spot areas. In this paper we investigate the organisation of spot areas within sunspot groups. In particular, we analysed the ratio (R) of the area of the biggest spot (Abig_spot) inside a group, to the total area of that group (Agroup). We used sunspot observations from Kislovodsk, Pulkovo, and Debrecen observatories, together covering solar cycles 17–24. We find that at the time when the group area reaches its maximum, the single biggest spot in a group typically occupies about 60% of the group area. For half of all groups, R lies in the range between roughly 50% and 70%. We also find R to change with Agroup, such that R reaches a maximum of about 0.65 for groups with Agroup ≈ 200 μHem and then remains at about 0.6 for larger groups. Our findings imply a scale-invariant emergence pattern, providing an observational constraint on the emergence process. Furthermore, extrapolation of our results to larger sunspot groups may have a bearing on the giant unresolved starspot features found in Doppler images of highly active Sun-like stars. Our results suggest that such giant features are composed of multiple spots, with the largest spot occupying roughly 55–75% of the total group area (i.e., the area of the giant starspots seen in Doppler images).

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Section: Discussionmentioning

confidence: 99%

On the size distribution of spots within sunspot groups

Mandal

Krivova

Cameron

et al. 2021

A&A

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“…This leaves an integral along the photosphere. As is shown in Cameron & Schüssler (2020), a straightforward implication of the empirical flux transport model is that this integral is determined by flux emergence events. We also note that the φ-component of the axisymmetric magnetic field seen at the solar photosphere corresponds to flux emerging through the surface (Cameron et al 2018).…”

Section: Toroidal Flux Budgetsmentioning

confidence: 96%

The crucial role of surface magnetic fields for stellar dynamos: ϵ Eridani, 61 Cygni A, and the Sun

Jeffers

Cameron

Marsden

et al. 2022

A&A

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Cool main-sequence stars, such as the Sun, have magnetic fields which are generated by an internal dynamo mechanism. In the Sun, the dynamo mechanism produces a balance between the amounts of magnetic flux generated and lost over the Sun’s 11-year activity cycle and it is visible in the Sun’s different atmospheric layers using multi-wavelength observations. We used the same observational diagnostics, spanning several decades, to probe the emergence of magnetic flux on the two close by, active- and low-mass K dwarfs: 61 Cygni A and ϵ Eridani. Our results show that 61 Cygni A follows the Solar dynamo with a regular cycle at all wavelengths, while ϵ Eridani represents a more extreme level of the Solar dynamo, while also showing strong Solar-like characteristics. For the first time we show magnetic butterfly diagrams for stars other than the Sun. For the two K stars and the Sun, the rate at which the toroidal field is generated from surface poloidal field is similar to the rate at which toroidal flux is lost through flux emergence. This suggests that the surface field plays a crucial role in the dynamos of all three stars. Finally, for ϵ Eridani, we show that the two chromospheric cycle periods, of ∼3 and ∼13 years, correspond to two superimposed magnetic cycles.

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“…In that work ARs were ordered by their individual contributions to the global axial dipole moment: it was found that, far from being dominated by a few ARs with the largest contributions, the global dipole moment built up during a cycle cannot be reproduced without taking into account a large number (hundreds) of ARs. In another recent work Cameron & Schüssler (2020) found that even ephemeral active regions contribute to the net toroidal flux loss from the Sun by an amount comparable to the contribution of large active regions. By analogy, this opens the possibility that ephemeral ARs may also contribute to the global poloidal field by a non-negligible amount, though statistical studies of the orientation of ephemeral ARs are unfortunately rare (cf.…”

Section: General Introductionmentioning

confidence: 90%

Towards an algebraic method of solar cycle prediction

Nagy

Petrovay

Lemerle

et al. 2020

J. Space Weather Space Clim.

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An algebraic method for the reconstruction and potentially prediction of the solar dipole moment value at sunspot minimum (known to be a good predictor of the amplitude of the next solar cycle) was suggested in the first paper in this series. The method sums up the ultimate dipole moment contributions of individual active regions in a solar cycle: for this, detailed and reliable input data would in principle be needed for thousands of active regions in a solar cycle. To reduce the need for detailed input data, here we propose a new active region descriptor called ARDoR (Active Region Degree of Rogueness). In a detailed statistical analysis of a large number of activity cycles simulated with the 2x2D dynamo model we demonstrate that ranking active regions by decreasing ARDoR, for a good reproduction of the solar dipole moment at the end of the cycle it is sufficient to consider the top N regions on this list explicitly, where N is a relatively low number, while for the other regions the ARDoR value may be set to zero. E.g., with N =5 the fraction of cycles where the dipole moment is reproduced with an error exceeding ±30% is only 12%, significantly reduced with respect to the case N =0, i.e. ARDoRs set to zero for all active regions, where this fraction is 26%. This indicates that stochastic effects on the intercycle variations of solar activity are dominated by the effect of a low number of large "rogue" active regions, rather than the combined effect of numerous small ARs. The method has a potential for future use in solar cycle prediction.

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Loss of toroidal magnetic flux by emergence of bipolar magnetic regions

Cited by 12 publications

References 29 publications

On the size distribution of spots within sunspot groups

On the size distribution of spots within sunspot groups

The crucial role of surface magnetic fields for stellar dynamos: ϵ Eridani, 61 Cygni A, and the Sun

Towards an algebraic method of solar cycle prediction

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