Convective Nature of Sunspot Penumbral Filaments: Discovery of Downflows in the Deep Photosphere

Joshi, Jayant; Pietarila, A.; Hirzberger, J.; Solanki, S. K.; Cuadrado, R. Aznar; Merenda, L.

doi:10.1088/2041-8205/734/1/l18

Cited by 44 publications

(60 citation statements)

References 30 publications

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“…As a consequence, magnetic field with inverse polarity and downflow velocities should be observed all along the boundaries of bright penumbral filaments. While observational evidence for convective downflows in the whole penumbra has been recently reported (Scharmer et al 2011;Scharmer & Henriques 2012;Joshi et al 2011), the reversed flux has only been observed in the outer penumbra (Westendorp Plaza et al 1997del Toro Iniesta et al 2001). But even with the highest spatial resolution spectropolarimetry, we have been unable to observe them in the inner penumbra (Langhans et al 2005).…”

Section: Introductionmentioning

confidence: 52%

“…We can assess that our inverse profiles do not come from such an artificial effect for two reasons. First, we have undercorrected our data, because the used PSF is a lower limit of the real one (see, for instance, Joshi et al 2011). As a consequence, the continuum contrast has only changed from 6.3% in the original data to 11.8% in the deconvolved data.…”

Section: Resultsmentioning

confidence: 99%

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Returning magnetic flux in sunspot penumbrae

Cobo

Ramos

2012

A&A

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Aims. We study the presence of reversed polarity magnetic flux in sunspot penumbra.Methods. We applied a new regularized method to deconvolve spectropolarimetric data observed with the spectropolarimeter SP onboard Hinode. The new regularization is based on a principal component decomposition of the Stokes profiles. The resulting Stokes profiles were inverted to infer the magnetic field vector using SIR. Results. We find, for the first time, reversed polarity fields at the border of many bright penumbral filaments in the whole penumbra.

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Section: Introductionmentioning

confidence: 52%

Section: Resultsmentioning

confidence: 99%

Returning magnetic flux in sunspot penumbrae

Cobo

Ramos

2012

A&A

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“…Contrary to the claims of Franz & Schlichenmaier (2009 and Puschmann et al (2010a), the presence of downflows in the inner penumbra has been reported by Sánchez Almeida et al (2007), Joshi et al (2011), Scharmer et al (2011) and Scharmer & Henriques (2012 1 . In a recent study, Scharmer et al (2013) report narrow downflow lanes to be located at the boundaries between spines and inter-spines.…”

Section: Structure Of Penumbral Filamentsmentioning

confidence: 64%

“…Indirect support for azimuthal convection was put forward by Ichimoto et al (2007a), Zakharov et al (2008), Spruit et al (2010), Bharti et al (2010), although an alternative explanation of some of these observations in terms of waves has also been provided (Bharti et al 2012). Recent observations from the Swedish Solar Telescope (SST: Scharmer et al 2003)/CRisp Imaging Spectro-Polarimeter (CRISP) showed downflows in the inner penumbra and a qualitative association of upflows with hot and downflows with cool gas in the deep photosphere (Joshi et al 2011;Scharmer et al 2011;Scharmer & Henriques 2012). A&A 557, A25 (2013) However, some other researchers did not detect such flow patterns (Franz & Schlichenmaier 2009;Bellot Rubio et al 2010;Puschmann et al 2010a).…”

Section: Introductionmentioning

confidence: 99%

Structure of sunspot penumbral filaments: a remarkable uniformity of properties

Tiwari

Noort

Lagg

et al. 2013

A&A

205

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Context. The sunspot penumbra comprises numerous thin, radially elongated filaments that are central for heat transport within the penumbra, but whose structure is still not clear. Aims. We aim to investigate the fine-scale structure of these penumbral filaments. Methods. We perform a depth-dependent inversion of spectropolarimetric data of a sunspot very close to solar disk center obtained by Solar Optical Telescope/Spectropolarimeter onboard the Hinode spacecraft. We have used a recently developed, spatially coupled 2D inversion scheme, which allows us to analyze the fine structure of individual penumbral filaments up to the diffraction limit of the telescope.Results. Filaments of different sizes in all parts of the penumbra display very similar magnetic field strengths, inclinations, and velocity patterns. The temperature structure is also similar, although the filaments in the inner penumbra have cooler tails than those in the outer penumbra. The similarities allowed us to average all these filaments and to subsequently extract the physical properties common to all of them. This average filament shows upflows associated with an upward-pointing field at its inner, umbral end (head) and along its axis, as well as downflows along the lateral edge and strong downflows in the outer end (tail) associated with a nearly vertical, strong, and downward-pointing field. The upflowing plasma is significantly, i.e., up to 800 K, hotter than the downflowing plasma. The hot, tear-shaped head of the averaged filament can be associated with a penumbral grain. The central part of the filament shows nearly horizontal fields with strengths in the range of 1 kG. The field above the filament converges, whereas a diverging trend is seen in the deepest layers near the head of the filament. The fluctuations in the physical parameters along and across the filament increase rapidly with depth. Conclusions. We put forward a unified observational picture of a sunspot penumbral filament. It is consistent with such a filament being a magneto-convective cell, in line with recent magnetohydrodynamic simulations. The uniformity of its properties over the penumbra sets constraints on penumbral models and simulations. The complex and inhomogeneous structure of the filament provides a natural explanation for a number of long-running controversies in the literature.

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“…It has also been confirmed that the Evershed flow can reach supersonic and super-Alvénic values, not only on the outer penumbra (Borrero et al 2005;van Noort et al 2013), but also close to the umbra (del Toro Iniesta et al 2001;Bellot Rubio et al 2004) and has a strong upflowing component at the inner penumbra that turns into a downflowing component at larger radial distances (Franz & Schlichenmaier 2009Tiwari et al 2013). Finally, there is strong evidence for an additional component of the velocity field in intraspines that appears as convective upflows along the center of the intraspines that turns into downflows at the filaments' edges (Zakharov et al 2008;Joshi et al 2011;Scharmer et al 2011;Tiwari et al 2013). These downflows seem capable of dragging the magnetic field lines and turning them back into the solar surface (Ruiz Cobo & Asensio Ramos 2013;Scharmer et al 2013).…”

Section: Introductionmentioning

confidence: 99%

Deep probing of the photospheric sunspot penumbra: no evidence of field-free gaps

Borrero

Ramos

Collados

et al. 2016

A&A

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Context. Some models for the topology of the magnetic field in sunspot penumbrae predict the existence of field-free or dynamically weak-field regions in the deep Photosphere. Aims. To confirm or rule out the existence of weak-field regions in the deepest photospheric layers of the penumbra. Methods. The magnetic field at log τ5 = 0 is investigated by means of inversions of spectropolarimetric data of two different sunspots located very close to disk center with a spatial resolution of approximately 0.4-0.45 ′′ . The data have been recorded using the GRIS instrument attached to the 1.5-meters GREGOR solar telescope at El Teide observatory. It includes three Fe i lines around 1565 nm, whose sensitivity to the magnetic field peaks at half a pressure-scale-height deeper than the sensitivity of the widely used Fe i spectral line pair at 630 nm. Prior to the inversion, the data is corrected for the effects of scattered light using a deconvolution method with several point spread functions. Results. At log τ5 = 0 we find no evidence for the existence of regions with dynamically weak (B < 500 Gauss) magnetic fields in sunspot penumbrae. This result is much more reliable than previous investigations done with Fe i lines at 630 nm. Moreover, the result is independent of the number of nodes employed in the inversion, and also independent of the point spread function used to deconvolve the data, and does not depend on the amount of straylight (i.e. wide-angle scattered light) considered.

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Convective Nature of Sunspot Penumbral Filaments: Discovery of Downflows in the Deep Photosphere

Cited by 44 publications

References 30 publications

Returning magnetic flux in sunspot penumbrae

Returning magnetic flux in sunspot penumbrae

Structure of sunspot penumbral filaments: a remarkable uniformity of properties

Deep probing of the photospheric sunspot penumbra: no evidence of field-free gaps

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