The Analysis of Penumbral Fine Structure Using an Advanced Inversion Technique

Jurčák, J.; Rubio, L. Bellot; Ichimoto, Kiyoshi; Katsukawa, Y.; Lites, B. W.; Nagata, Shinji; Shimizu, Toshifumi; Suematsu, Y.; Tarbell, T. D.; Title, A. M.; Tsuneta, S.

doi:10.1093/pasj/59.sp3.s601

Cited by 33 publications

(32 citation statements)

References 17 publications

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“…The magnetic field strength in the upflow regions is comparable to the values reported by Sobotka & Jurčák (2009) for penumbral bright grains and also to values found for the inner penumbra by e.g., Jurčák et al (2007), Borrero et al (2006), andBellot Rubio et al (2004). The agreement with previous results make the simplified inversion trustworthy at least for the upflow structures that are spatially larger than the downflow patches.…”

Section: Plasma Properties In the Downflow Patchessupporting

confidence: 88%

Temporal downflows in a penumbra

Jurčák

Katsukawa

2010

A&A

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Aims. We analyze temporal downflow patches that are located in a penumbra and have the same polarity of the magnetic field as a sunspot umbra. Methods. The repetitive 2 wide raster scans of penumbral regions that are taken with one minute cadence by the Hinode spectropolarimeter are used to detect the line-of-sight velocities in the penumbra from enhanced signals in the wings of Stokes V profiles. The lifetimes and positions within penumbra of the identified downflow patches are investigated. The plasma properties of the downflow patches are determined using the inversions of the observed Stokes profiles. Results. The temporal downflows have lifetimes of up to fourteen minutes. Some of them are related to the disappearance or weakening of nearby upflow regions or to the chromospheric brightenings. The downflows take place in regions with stronger and more vertical magnetic fields than the upflow regions.

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Section: Plasma Properties In the Downflow Patchessupporting

confidence: 88%

Temporal downflows in a penumbra

Jurčák

Katsukawa

2010

A&A

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“…This gives in total 19 free parameters for 329 wavelength points ×4 Stokes parameters (=1316 measurement values), which, however, are not all fully independent (see the discussion in Sánchez Almeida 2005). SIRGAUS has been used in a number of investigations (Bellot Rubio 2003;Beck 2006;Jurcák et al 2007;Cabrera Solana et al 2008;Ishikawa et al 2010). The main difference between the standard version of SIR and SIRGAUS is that spectral lines cannot be treated as blends of each other, i.e., the mutual influence of the line wings on the neighboring lines is not included.…”

Section: Discussionmentioning

confidence: 99%

“…A&A 525, A133 (2011) One of the suggested configurations for the threedimensional organization of the penumbral magnetic fields is the so-called "uncombed" penumbra (Solanki & Montavon 1993), where less inclined field lines wind around horizontal flow channels (see for instance Borrero et al 2008). This configuration has been taken up by modeling (Thomas & Montesinos 1993;Schlichenmaier et al 1998;Schlichenmaier & Collados 2002;Müller et al 2002;Borrero et al 2004;Müller et al 2006) 1 and inversion schemes since it is one of the few approaches that reproduces the observed NCP (e.g., Martínez Pillet 2000; Borrero et al 2006;Beck 2006;Jurcák et al 2007;Borrero et al 2007). Another approach reproducing the observed NCP is the so-called micro-structured magnetic atmosphere hypothesis (MISMA;Sanchez Almeida 1998;Sánchez Almeida 2001, 2005 that proposes a fine structure of the magnetic field on scales of a few km.…”

Section: Introductionmentioning

confidence: 99%

An uncombed inversion of multiwavelength observations reproducing the net circular polarization in a sunspot’s penumbra

Beck

2010

A&A

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Context. The penumbra of sunspots has a complex magnetic field topology whose three-dimensional organization remains unclear after more than a century of investigation. Aims. I derive a geometrical model of the penumbral magnetic field topology from an uncombed inversion setup designed to reproduce the net circular polarization (NCP) of simultaneous spectra in near-infrared (IR; 1.56 μm) and visible (VIS; 630 nm) spectral lines. Methods. I inverted the co-spatial spectra of five photospheric lines with a model that mimicked vertically interlaced magnetic fields with two distinct components, labeled background field and flow channels because of their characteristic properties (flow velocity, field inclination). The flow channels were modeled as a perturbation of the constant background field with a Gaussian shape using the SIRGAUS code. The location and extension of the Gaussian perturbation in the optical depth scale retrieved by the inversion code were then converted to a geometrical height scale. By estimating the geometrical size of the flow channels, I investigated the relative amount of magnetic flux in the flow channels and the background field atmosphere.Results. The uncombed model is able to reproduce the NCP well on the limb side of the spot and less successfully on the center side; the VIS lines are better reproduced than the near-IR lines. I find that the Evershed flow happens along nearly horizontal field lines close to the solar surface given by optical depth unity. The magnetic flux that is related to the flow channels constitutes about 20−50% of the total magnetic flux in the penumbra. Conclusions. The gradients that can be produced by a Gaussian perturbation are too small for a perfect reproduction of the NCP in the IR lines with their small formation height range, where a step function seems to be required. Two peculiarities of the observed NCP, a sign change in the NCP of the VIS lines on the center side and a ring structure around the umbra with opposite signs of the NCP in the Ti i line at 630.37 nm and the Fe i line at 1565.2 nm, deserve closer attention in future modeling attempts. The large fraction of magnetic flux related to the flow channel component could suffice to replenish the penumbral radiative losses in the flux tube picture.

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“…The inward flows are determined by the LCT method from the apparent motions of bright penumbral grains. As these structures are confined to the low photosphere (Jurčák et al 2007;Sobotka & Jurčák 2009), they are prominent in the G-band filtergrams but not in the Ca ii H images. Therefore, the inward motions are weaker and occupy smaller areas in Ca ii H. The motion patterns of the orphan penumbra are also similar in the upper and lower photosphere (Figs.…”

Section: Brightness and Apparent Motionsmentioning

confidence: 97%

Orphan penumbrae: Submerging horizontal fields

Jurčák

Rubio

Sobotka

2014

A&A

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Aims. We investigate the properties of orphan penumbrae, which are photospheric filamentary structures observed in active regions near polarity inversion lines that resemble the penumbra of regular sunspots but are not connected to any umbra. Methods. We use Hinode data from the Solar Optical Telescope to determine the properties of orphan penumbrae. Spectropolarimetric data are employed to obtain the vector magnetic field and line-of-sight velocities in the photosphere. Magnetograms are used to study the overall evolution of these structures, and G-band and Ca ii H filtergrams are to investigate their brightness and apparent horizontal motions.Results. Orphan penumbrae form between regions of opposite polarity in places with horizontal magnetic fields. Their magnetic configuration is that of Ω-shaped flux ropes. In the two cases studied here, the opposite-polarity regions approach each other with time and the whole structure submerges as the penumbral filaments disappear. Orphan penumbrae are very similar to regular penumbrae, including the existence of strong gas flows. Therefore, they could have a similar origin. The main difference between them is the absence of a "background" magnetic field in orphan penumbrae. This could explain most of the observed differences. Conclusions. The fast flows we detect in orphan penumbrae may be caused by the siphon flow mechanism. Based on the similarities between orphan and regular penumbrae, we propose that the Evershed flow is also a manifestation of siphon flows.

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The Analysis of Penumbral Fine Structure Using an Advanced Inversion Technique

Cited by 33 publications

References 17 publications

Temporal downflows in a penumbra

Temporal downflows in a penumbra

An uncombed inversion of multiwavelength observations reproducing the net circular polarization in a sunspot’s penumbra

Orphan penumbrae: Submerging horizontal fields

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