``Explosion'' and Intensification of Magnetic Flux Tubes

Moreno‐Insertis, F.; Caligari, P.; Schuessler, M.

doi:10.1086/176357

Cited by 65 publications

(49 citation statements)

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“…The maximum field strength of a flux tube that can be stored at a given latitude in the overshoot layer depends very sensitively on the value of δ, which is about −10 −4 to −10 −5 . Small variations in δ of about −10 −4 may decide whether a flux tube becomes unstable at 2 × 10 4 G or at 10 5 G. This makes a great difference, because flux tubes that do not reach a strength close to 10 5 G before entering the convection zone cannot reach the solar surface as a coherent structure and therefore cannot form sunspots (Moreno-Insertis et al 1995). Thus the tiny tidal effect could influence the magnetic storage capacity of the tachocline by modifying the stratification of entropy (δ), and thereby altering the maximum field strength of the flux tubes that can be stored there.…”

Section: Discussionmentioning

confidence: 99%

Is there a planetary influence on solar activity?

Abreu

Beer

Ferriz-Mas

et al. 2012

A&A

147

189

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Context. Understanding the Sun's magnetic activity is important because of its impact on the Earth's environment. Direct observations of the sunspots since 1610 reveal an irregular activity cycle with an average period of about 11 years, which is modulated on longer timescales. Proxies of solar activity such as 14 C and 10 Be show consistently longer cycles with well-defined periodicities and varying amplitudes. Current models of solar activity assume that the origin and modulation of solar activity lie within the Sun itself; however, correlations between direct solar activity indices and planetary configurations have been reported on many occasions. Since no successful physical mechanism was suggested to explain these correlations, the possible link between planetary motion and solar activity has been largely ignored. Aims. While energy considerations clearly show that the planets cannot be the direct cause of the solar activity, it remains an open question whether the planets can perturb the operation of the solar dynamo. Here we use a 9400 year solar activity reconstruction derived from cosmogenic radionuclides to test this hypothesis. Methods. We developed a simple physical model for describing the time-dependent torque exerted by the planets on a non-spherical tachocline and compared the corresponding power spectrum with that of the reconstructed solar activity record. Results. We find an excellent agreement between the long-term cycles in proxies of solar activity and the periodicities in the planetary torque and also that some periodicities remain phase-locked over 9400 years. Conclusions. Based on these observations we put forward the idea that the long-term solar magnetic activity is modulated by planetary effects. If correct, our hypothesis has important implications for solar physics and the solar-terrestrial connection.

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Section: Discussionmentioning

confidence: 99%

Is there a planetary influence on solar activity?

Abreu

Beer

Ferriz-Mas

et al. 2012

A&A

147

189

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“…The transient horizontal fields revealed by Hinode in our study suggest the possibility of such a local dynamo process (Cattaneo 1999;Vögler & Schüssler 2007). An alternative physical picture is presented by the extended fields caused by an exploding magnetic structure (Moreno-Insertis et al 1995) and/or by horizontal magnetic fields that failed to emerge (Magara 2001).…”

Section: Discussionmentioning

confidence: 99%

Transient horizontal magnetic fields in solar plage regions

Ishikawa

Tsuneta

Ichimoto

et al. 2008

A&A

108

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Aims. We report the discovery of isolated, small-scale emerging magnetic fields in a plage region with the Solar Optical Telescope aboard Hinode. Methods. Spectro-polarimetric observations were carried out with a cadence of 34 s for the plage region located near disc center. The vector magnetic fields are inferred by Milne-Eddington inversion. Results. The observations reveal widespread occurrence of transient, spatially isolated horizontal magnetic fields. The lateral extent of the horizontal magnetic fields is comparable to the size of photospheric granules. These horizontal magnetic fields seem to be tossed about by upflows and downflows of the granular convection. We also report an event that appears to be driven by the magnetic buoyancy instability. We refer to buoyancy-driven emergence as type 1 and convection-driven emergence as type 2. Although both events have magnetic field strengths of about 600 G, the filling factor of type 1 is a factor of two larger than that of type 2. Conclusions. Our finding suggests that the granular convection in the plage regions is characterized by a high rate of occurrence of granular-sized transient horizontal fields.

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“…Then, external convective motions are able to control the evolution of the sub-surface flux tube, perhaps a few Mm below the photosphere, and the upper, emerged, part loses knowledge of its connection at the base of the convective zone (Fan et al, 1994;Moreno-Insertis et al, 1995;Schüssler and Rempel, 2005). The photospheric field is then effectively disconnected from its roots.…”

Section: Disconnection From Toroidal Rootsmentioning

confidence: 99%

Evolution of Active Regions

Driel-Gesztelyi

Green

2015

Living Rev. Sol. Phys.

265

131

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The evolution of active regions (AR) from their emergence through their long decay process is of fundamental importance in solar physics. Since large-scale flux is generated by the deepseated dynamo, the observed characteristics of flux emergence and that of the subsequent decay provide vital clues as well as boundary conditions for dynamo models. Throughout their evolution, ARs are centres of magnetic activity, with the level and type of activity phenomena being dependent on the evolutionary stage of the AR. As new flux emerges into a pre-existing magnetic environment, its evolution leads to re-configuration of small-and large-scale magnetic connectivities. The decay process of ARs spreads the once-concentrated magnetic flux over an ever-increasing area. Though most of the flux disappears through small-scale cancellation processes, it is the remnant of large-scale AR fields that is able to reverse the polarity of the poles and build up new polar fields. In this Living Review the emphasis is put on what we have learned from observations, which is put in the context of modelling and simulation efforts when interpreting them. For another, modelling-focused Living Review on the sub-surface evolution and emergence of magnetic flux see Fan (2009). In this first version we focus on the evolution of dominantly bipolar ARs. 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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``Explosion'' and Intensification of Magnetic Flux Tubes

Cited by 65 publications

References 0 publications

Is there a planetary influence on solar activity?

Is there a planetary influence on solar activity?

Transient horizontal magnetic fields in solar plage regions

Evolution of Active Regions

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