Dynamo action in stratified convection with overshoot

Nordlund, Åke; Brandenburg, Axel; Jennings, R. L.; Rieutord, M.; Ruokolainen, Juha; Stein, R. F.; Tuominen, I.

doi:10.1086/171465

Cited by 222 publications

(168 citation statements)

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“…It is still a question whether or not ephemeral regions (ERs, Harvey and Martin, 1973;Harvey, 1993) are simply the small-scale end of a broad size-spectrum and whether their characteristics and origin are the same as larger ARs (Harvey and Martin, 1973) or if they are generated by a local dynamo process and/or are recycled flux from dispersing ARs (Nordlund et al, 1992). The latitudinal distribution of ephemeral regions extends well beyond the activity belt populated by ARs, and their tilt angle distribution is becoming increasingly random with decreasing flux content, which seems to support their origin in a local dynamo.…”

Section: Lifetimementioning

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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Section: Lifetimementioning

confidence: 99%

Evolution of Active Regions

Driel-Gesztelyi

Green

2015

Living Rev. Sol. Phys.

265

131

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“…Ephemeral regions are believed to have a common origin with active regions in the global dynamo (Harvey 1993), but it is also thought that they are generated locally everywhere by turbulent convection near the surface (Nordlund et al 1992). A third way involves both the global dynamo and flux processing in the convective envelope.…”

Section: Sunspots and Ephemeral Regionsmentioning

confidence: 99%

Solar Weather Event Modelling and Prediction

et al. 2009

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Key drivers of solar weather and mid-term solar weather are reviewed by considering a selection of relevant physics-and statistics-based scientific models as well as a selection of related prediction models, in order to provide an updated operational scenario for space weather applications. The characteristics and outcomes of the considered scientific and prediction models indicate that they only partially cope with the complex nature of solar activity for the lack of a detailed knowledge of the underlying physics. This is indicated by the fact that, on one hand, scientific models based on chaos theory and non-linear dynamics reproduce better the observed features, and, on the other hand, that prediction models based on statistics and artificial neural networks perform better. To date, the solar weather prediction success at most time and spatial scales is far from being satisfactory, but the forthcoming ground-and space-based high-resolution observations can add fundamental tiles to the modelling and predicting frameworks as well as the application of advanced mathematical approaches in the analysis of diachronic solar observations, that are a must to provide comprehensive and homogeneous data sets.

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“…However, the numerical simulations which are now possible lead to the opposite phenomenon: the mean magnetic flux is pumped downwards (Dorch & Nordlund 2001;Thomas et al 2002;Ossendrijver et al 2002;Ziegler & Rüdiger 2003). It seems indeed as would the downward pumping of the magnetic field be the most prominent feature of the rotating magnetoconvection (Nordlund et al 1992). On the other hand, the penetration depth of the overshooting convection into the stable region below the convection zone appears to be very small (see Ziegler & Rüdiger 2003).…”

Section: Introductionmentioning

confidence: 95%

Advection‐dominated solar dynamo model with two‐cell meridional flow and a positive α ‐effect in the tachocline

Bonanno¹,

Elstner

Belvedère

2006

Astron Nachr

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Most probably the sunspot cycle period is ruled by a meridional flow located near the base of the convection zone (Hathaway et al. 2003). On the other hand, if the eddy diffusivity is low enough, dramatic modification of the standard α 2 Ω-dynamo by the meridional flow are expected. In this paper we shall discuss the dependence of periods, dynamo numbers and the sign of the current helicity as a function of the magnetic Reynolds number for a double cell meridional circulation and for a positive α-effect at the base of the convection zone. The dynamo action occurs at lower latitudes and its location is at the interface between equatorward and poleward motions near the base of the convection zone. In spite of the complexity of the flow pattern, our simulations show that the resulting dynamo action reproduces several observed features of the solar cycle.

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Dynamo action in stratified convection with overshoot

Cited by 222 publications

References 0 publications

Evolution of Active Regions

Evolution of Active Regions

Solar Weather Event Modelling and Prediction

Advection‐dominated solar dynamo model with two‐cell meridional flow and a positive α ‐effect in the tachocline

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