Formation of a penumbra in a decaying sunspot

Louis, Rohan E.; Mathew, Shibu K.; Puschmann, K. G.; Beck, C.; Balthasar, H.

doi:10.1051/0004-6361/201321314

Cited by 9 publications

(5 citation statements)

References 25 publications

(26 reference statements)

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“…A possible origin for this structure might be related to a magnetic field rearrangement occurring in the AR. Changes in the magnetic field topology have been recently invoked to explain the formation of penumbral filaments also in mature spots (Louis et al 2013;Verma et al 2018;Romano et al 2019). The overlying flux rope could stabilize a configuration where strong horizontal fields are present for a quite long time (some days), explaining the lifetime of the observed UF.…”

Section: Discussionmentioning

confidence: 99%

Properties of the Umbral Filament Observed in Active Region NOAA 12529

Guglielmino¹,

Romano

Cobo

et al. 2019

ApJ

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Recent observations of the solar photosphere revealed the presence of elongated filamentary bright structures inside sunspot umbrae, called umbral filaments (UFs). These features differ in morphology, magnetic configuration, and evolution from light bridges that are usually observed to intrude in sunspots. To characterize an UF observed in the umbra of the giant leading sunspot of active region NOAA 12529, we analyze high-resolution observations taken in the photosphere with the spectropolarimeter aboard the Hinode satellite and in the upper chromosphere and transition region with the IRIS telescope. The results of this analysis definitely rule out the hypothesis that the UF might be a kind of light bridge. In fact, we find no field-free or low-field strength region cospatial to the UF. Conversely, we recognize the presence of a strong horizontal field larger than 2500 G, a significant portion of the UF with opposite polarity with respect to the surroundings, and filaments in the upper atmospheric layers corresponding to the UF in the photosphere. These findings suggest that this structure is the photospheric manifestation of a flux rope hanging above the sunspot and forming penumbral-like filaments within the umbra via magneto-convection. This reinforces a previously proposed scenario.

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Section: Discussionmentioning

confidence: 99%

Properties of the Umbral Filament Observed in Active Region NOAA 12529

Guglielmino¹,

Romano

Cobo

et al. 2019

ApJ

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“…In the upper solar atmosphere the direction of the EF reverses and flows into the sunspot and as such is referred to as the reverse/inverse EF (St. John, 1913). However, the formation of a penumbra is sometimes associated with flows that have an opposite sign as the EF in the photosphere (Schlichenmaier et al, 2012) and can even be supersonic (Louis et al, 2013). Bellot Rubio et al (2008) showed an example of an an oppositely directed EF associated with decaying penumbral filaments.…”

Section: Introductionmentioning

confidence: 99%

Anomalous flows in a sunspot penumbra

Louis

Beck

Mathew

et al. 2014

A&A

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Context. The photospheric Evershed flow is a distinct characteristic of penumbrae that is closely associated with the photometric and magnetic structure of sunspots. Aims. We analyse the properties of an anomalous flow in the photosphere in a sunspot penumbra and compare it with those of the regular Evershed flow. Methods. High-resolution spectropolarimetric observations of active region NOAA 11271 were obtained with the spectro-polarimeter (SP) on board Hinode. We used the magnetic field properties derived by a Milne-Eddington inversion. In addition, we used Ca II H images obtained by the broad-band filter instrument to study the low chromospheric response to the photospheric structure and Dopplergrams from the Helioseismic and Magnetic Imager to follow the evolution of the photospheric flows.Results. We detect a blueshifted feature that appeared on the limb-side penumbra of a sunspot and that was present intermittently during the next two hours. It exhibited a maximum blueshift of 1.6 km s −1 , an area of 5.2 arcsec 2 , and a maximum uninterrupted lifetime of 1 h. The blueshifted feature, when present, lies parallel to redshifts. Both blue-and redshifts flank a highly inclined or horizontal magnetic structure that is radially oriented in the penumbra. The low-cadence SP maps reveal changes in size, radial position in the penumbra, and line-of-sight (LOS) velocity of the blueshifted feature, from one scan to the next. There was an increase of nearly 500 G in the field strength with the onset of the blueshifts, particularly when the LOS velocity in the feature exceeded 1.5 km s −1 . There was only a marginal reduction in the field inclination of about 10• with the increase in blueshifts. In the chromosphere, intense, arc-shaped brightenings were observed close to the location of the photospheric blueshifts, which extend from the edge of the umbral core to the penumbra-quiet Sun boundary. The intensity of these brightenings exceeds the background intensity by 30% to 65% with the strongest and largest brightenings observed about 30 min after the strongest blueshifts were detected at the photosphere. The close spatial proximity of the two phenomenon strongly suggests a causal relationship. Conclusions. The blueshifted feature represents plasma motion that could be related to a magnetic structure that rises in the solar atmosphere and subsequently reconnects with the ambient chromospheric magnetic field of the sunspot or an inverse Evershed flow, which would be unique in the photosphere. This transient phenomena is presumably related to the dynamic stability of the sunspot because the corresponding umbral core separated two days later at the location of the blueshifts and fragmented subsequently.

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“…Both studies agreed that the ongoing flux emergence around sunspot inhibited the formation of stable penumbra and suggested a "quiet" magnetic surrounding in the vicinity of a sunspot seems to facilitate the formation of stable penumbra on a dynamical timescale. In contrast, Louis et al (2013) found some stable penumbral filaments of a decaying sunspot formed after the newly emerged patch coalesced with the sunspot. Likewise, Murabito et al (2017) observed that the first stable penumbral sector around a pore formed in the flux emergence region.…”

Section: Introductionmentioning

confidence: 80%

The Formation and Decay of Sunspot Penumbrae in Active Region NOAA 12673

Yan²,

Wang³

et al. 2019

ApJ

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To better understand the formation and decay of sunspot penumbra, we studied the evolution of sunspots in the three regions of the active-region NOAA 12673 in detail. The evolution of sunspots in the three regions were all involved in the interaction of two magnetic field systems: the pre-existing magnetic field system and the later emerging magnetic field system. Through analyzing the photospheric magnetic field properties, it is found that the formation of the penumbra originated from the newly emerging magnetic bipole that were trapped in the photosphere. The change of magnetic fields in penumbra from horizontal to vertical can cause the disappearance of penumbra. The transformation of the magnetic field between the umbra and the penumbra is found and the outward moat flow around sunspot gradually decreased and vanished during the decay of sunspot. In addition, we found that the mean longitudinal magnetic strength in penumbra decreased and the mean transverse magnetic strength in penumbra increased with the increasing penumbral area during the formation of sunspots. However, during the decay of sunspots, the mean longitudinal magnetic strength in penumbra increased and the mean transverse magnetic strength in penumbra decreased with the decreasing penumbral area. Comparatively, the dependence of the area and the mean transverse/longitudinal magnetic field strength in umbra is not remarkable. These results reveal that the formation and decay process of umbra are different with penumbra.

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Formation of a penumbra in a decaying sunspot

Cited by 9 publications

References 25 publications

Properties of the Umbral Filament Observed in Active Region NOAA 12529

Properties of the Umbral Filament Observed in Active Region NOAA 12529

Anomalous flows in a sunspot penumbra

The Formation and Decay of Sunspot Penumbrae in Active Region NOAA 12673

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