Flux Pumping and Magnetic Fields in the Outer Penumbra of a Sunspot

Brummell, Nicholas H.; Tobias, Steven M.; Thomas, John H.; Weiss, N. O.

doi:10.1086/591640

Cited by 31 publications

(33 citation statements)

References 49 publications

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“…The downward transport of such U-loops, which allows the discharge of mass from the rising magnetic field, is related to the phenomenon known as turbulent pumping (Tobias et al 1998;Brummell et al 2002Brummell et al , 2008. Turbulent pumping manifests itself in terms of the vertical component of the Poynting flux of magnetic energy, which for ideal MHD is…”

Section: Discharge Of Mass From the Rising Magnetic Structurementioning

confidence: 99%

Simulation of the Formation of a Solar Active Region

Cheung

Rempel

Title

et al. 2010

ApJ

261

326

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We present a radiative magnetohydrodynamics simulation of the formation of an active region (AR) on the solar surface. The simulation models the rise of a buoyant magnetic flux bundle from a depth of 7.5 Mm in the convection zone up into the solar photosphere. The rise of the magnetic plasma in the convection zone is accompanied by predominantly horizontal expansion. Such an expansion leads to a scaling relation between the plasma density and the magnetic field strength such that B ∝ 1/2 . The emergence of magnetic flux into the photosphere appears as a complex magnetic pattern, which results from the interaction of the rising magnetic field with the turbulent convective flows. Small-scale magnetic elements at the surface first appear, followed by their gradual coalescence into larger magnetic concentrations, which eventually results in the formation of a pair of opposite polarity spots. Although the mean flow pattern in the vicinity of the developing spots is directed radially outward, correlations between the magnetic field and velocity field fluctuations allow the spots to accumulate flux. Such correlations result from the Lorentz-force-driven, counterstreaming motion of opposite polarity fragments. The formation of the simulated AR is accompanied by transient light bridges between umbrae and umbral dots. Together with recent sunspot modeling, this work highlights the common magnetoconvective origin of umbral dots, light bridges, and penumbral filaments.

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Section: Discharge Of Mass From the Rising Magnetic Structurementioning

confidence: 99%

Simulation of the Formation of a Solar Active Region

Cheung

Rempel

Title

et al. 2010

ApJ

261

326

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show abstract

“…To account for the filamentary structure of penumbrae, the following models have been proposed, i.e., the embedded or rising flux tube model (Solanki & Mondavon 1993, Schlichenmaier et al 1998 in which the Evershed flow channels are explained as rising flux tubes embedded in more vertical background magnetic fields in the penumbra, the gappy penumbral model in which the bright penumbral filaments are regarded as manifestations of the protrusion of non-magnetized, convecting hot gas into the oblique background fields of the penumbra, and the downward pumping model (Thomas et al 2002, Brummell et al 2008 in which the penumbral fine structure is created by localized submergence of penumbral fields that are forced by the photospheric convection around the outer edge of penumbrae. There is still no consensus on the physical nature and origin of the penumbral fine structures.…”

Section: Introductionmentioning

confidence: 99%

The Evershed Effect with SOT/Hinode

Ichimoto¹,

Sot²,

Hinode-team³

2009

Magnetic Coupling Between the Interior and Atmosphere of the Sun

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Summary. The Solar Optical Telescope onboard Hinode revealed the fine-scale structure of the Evershed flow and its relation to the filamentary structures of the sunspot penumbra. The Evershed flow is confined in narrow channels with nearly horizontal magnetic fields, embedded in a deep layer of the penumbral atmosphere. It is a dynamic phenomenon with flow velocity close to the photospheric sound speed. Individual flow channels are associated with tiny upflows of hot gas (sources) at the inner end and downflows (sinks) at the outer end. SOT/Hinode also discovered "twisting" motions of penumbral filaments, which may be attributed to the convective nature of the Evershed flow. The Evershed effect may be understood as a natural consequence of thermal convection under a strong, inclined magnetic field. Current penumbral models are discussed in the lights of these new Hinode observations.

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“…The scenario described in Section 4 for the formation of the penumbra and the returning flux tubes through flux pumping leads us to a magnetic field configuration in the outer penumbra roughly as depicted in the right-hand panel of Figure 3 ( Thomas et al 2006;Brummell et al 2008). This configuration, which we might describe as an "interleaved sheet" model, has vertical sheets of nearly horizontal magnetic field (dark filaments) interleaved between sheets of more vertical magnetic field (bright filaments).…”

Section: The Magnetic Field Configuration In the Penumbramentioning

confidence: 95%

“…In this picture, the sheets of horizontal field extend downward below the visible surface to a depth of, say, 5 Mm. (A simple estimate gives the depth of penetration equal to one-quarter of the width of the penumbra: Brummell et al 2008). Fig.…”

Section: The Magnetic Field Configuration In the Penumbramentioning

confidence: 99%

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Theoretical Models of Sunspot Structure and Dynamics

Thomas

2009

Magnetic Coupling Between the Interior and Atmosphere of the Sun

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Summary. Recent progress in theoretical modeling of a sunspot is reviewed. The observed properties of umbral dots are well reproduced by realistic simulations of magnetoconvection in a vertical, monolithic magnetic field. To understand the penumbra, it is useful to distinguish between the inner penumbra, dominated by bright filaments containing slender dark cores, and the outer penumbra, made up of dark and bright filaments of comparable width with corresponding magnetic fields differing in inclination by some 30 degrees and strong Evershed flows in the dark filaments along nearly horizontal or downward-plunging magnetic fields. The role of magnetic flux pumping in submerging magnetic flux in the outer penumbra is examined through numerical experiments, and different geometric models of the penumbral magnetic field are discussed in the light of high-resolution observations. Recent, realistic numerical MHD simulations of an entire sunspot have succeeded in reproducing the salient features of the convective pattern in the umbra and the inner penumbra. The siphon-flow mechanism still provides the best explanation of the Evershed flow, particularly in the outer penumbra where it often consists of cool, supersonic downflows.

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Flux Pumping and Magnetic Fields in the Outer Penumbra of a Sunspot

Cited by 31 publications

References 49 publications

Simulation of the Formation of a Solar Active Region

Simulation of the Formation of a Solar Active Region

The Evershed Effect with SOT/Hinode

Theoretical Models of Sunspot Structure and Dynamics

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