Formation of the Penumbra and Start of the Evershed Flow

Murabito, M.; Romano, P.; Guglielmino, Salvo L.; Zuccarello, F.; Solanki, S. K.

doi:10.3847/0004-637x/825/1/75

Cited by 43 publications

(54 citation statements)

References 54 publications

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“…In this Letter we propose that penumbra formation is The penumbra now occupies the entire AC and is not developed only at a small location near the CER. This penumbra formation is also analyzed by Romano et al (2013) and Murabito et al (2016).…”

Section: Introductionsupporting

confidence: 58%

The Pre-Penumbral Magnetic Canopy in the Solar Atmosphere

MacTaggart

Guglielmino²,

Zuccarello³

2016

ApJL

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Penumbrae are the manifestation of magnetoconvection in highly inclined (to the vertical direction) magnetic field. The penumbra of a sunspot tends to form, initially, along the arc of the umbra antipodal to the main region of flux emergence. The question of how highly inclined magnetic field can concentrate along the antipodal curves of umbrae, at least initially, remains to be answered. Previous observational studies have suggested the existence of some form of overlying magnetic canopy which acts as the progenitor for penumbrae. We propose that such overlying magnetic canopies are a consequence of how the magnetic field emerges into the atmosphere and are, therefore, part of the emerging region. We show, through simulations of twisted flux tube emergence, that canopies of highly inclined magnetic field form preferentially at the required locations above the photosphere.

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Section: Introductionsupporting

confidence: 58%

The Pre-Penumbral Magnetic Canopy in the Solar Atmosphere

MacTaggart

Guglielmino²,

Zuccarello³

2016

ApJL

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“…The very large line shifts and line splittings observed in the anomalous penumbral region, and the extensive area that the CEF spans, make this sunspot a rather unique one. The previously reported observations of CEFs by, e. g., Kleint & Sainz Dalda (2013); Louis et al (2014) have been mainly restricted to penumbral filaments of sunspots leading to flares, or have been found in forming penumbrae (Schlichenmaier et al 2012;Romano et al 2014;Murabito et al 2016). Kleint & Sainz Dalda (2013) propose two possible models to explain the observation of CEFs in the photosphere.…”

Section: Discussionmentioning

confidence: 95%

Normal and counter Evershed flows in the photospheric penumbra of a sunspot

Siu-Tapia

Lagg

Solanki

et al. 2017

A&A

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Context. The Evershed effect, a nearly horizontal outflow of material seen in the penumbrae of sunspots at the photospheric layers, is a common characteristic of well-developed penumbrae, but is still not well understood. Even less is known about photospheric horizontal inflows in the penumbra, also known as counter Evershed flows. Aims. Here we present a rare feature observed in the penumbra of the main sunspot of AR NOAA 10930. This spot displays the normal Evershed outflow in most of the penumbra, but harbors a fast photospheric inflow of material over a large sector of the disk-center penumbra. We investigate the driving forces of both, the normal and the counter Evershed flows. Methods. We invert the spectropolarimetric data from Hinode SOT/SP using the SPINOR 2D inversion code, which allows us to derive height-dependent maps of the relevant physical parameters in the sunspot. These maps show considerable fine structure. Similarities and differences between the normal Evershed outflow and the counter Evershed flow are investigated. Results. In both, the normal and the counter Evershed flows, the material flows from regions of weak (∼ 1.5 kG to ∼ 2 kG) to stronger fields. The sources and sinks of both penumbral flows display opposite field polarities; with the sinks (tails of filaments) harboring local enhancements in temperature, which are nonetheless colder than their sources (heads of filaments).Conclusions. The anti-correlation of the gradients in the temperature and magnetic pressure between the endpoints of the filaments from the two distinct penumbral regions is compatible with both the convective driver and the siphon flow scenarios. A geometrical scale of the parameters is necessary to determine which the dominant force driving the flows is.

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“…An overlying magnetic field in the chromosphere could trap newly emerging flux in the photosphere and prevent it from becoming vertical (Leka & Skumanich 1998;Lim et al 2013). Alternatively, a magnetic canopy in the chromosphere preceding the formation of the penumbra might sink down later and form the penumbra (Shimizu et al 2012;Romano et al 2013Romano et al , 2014Murabito et al 2016). A strong influence of the chromosphere on penumbra formation is further supported by numerical simulations, where the extent of the penumbra strongly depends on the details of the top boundary condition (Rempel 2012;Jurcak et al 2020).…”

Section: Introductionmentioning

confidence: 93%

No universal connection between the vertical magnetic field and the umbra-penumbra boundary in sunspots

Löptien

Lagg

Noort

et al. 2020

A&A

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Context. It has been reported that the boundary between the umbra and the penumbra of sunspots occurs at a canonical value of the strength of the vertical magnetic field, independently of the size of the spot. This critical field strength is interpreted to be the threshold for the onset of magnetoconvection. Aims. Here we investigate the reasons why this criterion, also called the Jurčák criterion in the literature, does not always identify the boundary between the umbra and the penumbra. Methods. We performed a statistical analysis of 23 sunspots observed with Hinode/SOT. We compared the properties of the continuum intensity and the vertical magnetic field between filaments and spines and how they vary between spots of different sizes. Results. We find that the inner boundary of the penumbra is not related to a universal value of the vertical magnetic field. The properties of spines and filaments vary between spots of different sizes. Both components are darker in larger spots and the spines exhibit a stronger vertical magnetic field. These variations of the properties of filaments and spines with the spot size are also the reason for the reported invariance in the averaged vertical magnetic field at 50% of the mean continuum intensity. Conclusions. The formation of filaments and the onset of magnetoconvection are not related to a canonical value of the strength of the vertical magnetic field. The seemingly unique magnetic field strength is rather an effect of the filling factor of spines and penumbral filaments.

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Formation of the Penumbra and Start of the Evershed Flow

Cited by 43 publications

References 54 publications

The Pre-Penumbral Magnetic Canopy in the Solar Atmosphere

The Pre-Penumbral Magnetic Canopy in the Solar Atmosphere

Normal and counter Evershed flows in the photospheric penumbra of a sunspot

No universal connection between the vertical magnetic field and the umbra-penumbra boundary in sunspots

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