Temporal downflows in a penumbra

Jurčák, J.; Katsukawa, Y.

doi:10.1051/0004-6361/201014722

Cited by 15 publications

(19 citation statements)

References 26 publications

(45 reference statements)

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“…Their lifetimes are typically comparable to or shorter than the temporal cadence (30 sec) of the FG observation. The penumbral microjets were found to roughly follow the orientation of background magnetic fields in the penumbra, and the inclination angle is from 40 • to 60 • with respect to the local vertical in the midpenumbra (Katsukawa et al, 2007;Jurčák & Katsukawa, 2008). The spot studied here was located at about 30 • away from the disk center in the observation.…”

Section: Chromospheric Brighteningsmentioning

confidence: 66%

“…This would make the detection in a SP observation less frequent. Temporal evolution of the downflow patches in penumbrae is studied in our another paper (Jurčák & Katsukawa, 2010). The difference of the spatial distribution between the limb-side and the center-side when the spot was located away from the disk center can be simply explained by orientation of the downflows and a projection effect.…”

Section: Summary and Discussionmentioning

confidence: 99%

“…Shibata et al, 2007). Katsukawa et al (2007) revealed that small-scale transient jetlike brightenings (referred to as penumbral microjets) occur ubiquitously in the chromosphere above sunspot penumbrae and suggested that magnetic reconnection in an interlaced magnetic field configuration is the most plausible explanation to these penumbral brightenings. It is therefore vital importance to accurately measure velocities and vector magnetic fields around the penumbral brightenings to ascertain their physical origin.…”

Section: Introductionmentioning

confidence: 99%

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A new type of small-scale downflow patches in sunspot penumbrae

Katsukawa

Jurčák

2010

A&A

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Context. Magnetic and flow structures in a sunspot penumbra are created by strong interplay between inclined magnetic fields and photospheric convection. They exhibit a complex nature that cannot always be explained by the well-known Evershed flow. Aims. A sunspot penumbra is observationally examined to reveal properties of small-scale flow structures and their relationship to the filamentary magnetic structures and the Evershed flow. We also study how the photospheric dynamics are related to chromospheric activities.Methods. This study is based on data analysis of spectro-polarimetric observations of photospheric Fe I lines with the Solar Optical Telescope aboard Hinode in a sunspot penumbra at different heliocentric angles. Vector magnetic fields and velocities are derived using the spectro-polarimetric data and a Stokes inversion technique. An observation with a Ca II H filtergram co-spatial and cotemporal with the spectro-polarimetric one is also used to study possible chromospheric responses. Results. We find small patches with downflows in the photospheric layers. The downflow patches have a size of 0.5 or smaller and a different geometrical configuration from the Evershed flow. The downflow velocity is about 1 km s −1 in the lower photspheric layers and is almost zero in the upper layers. Some of the downflow patches are associated with brightenings seen in Ca II H images. Conclusions. The downflows are possible observational signatures of downward flows driven by magnetic reconnection in the interlaced magnetic field configuration, where upward flows make brightenings in the chromosphere. Another possibility is that they are concentrated downward flows of overturning magnetoconvection.

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Section: Chromospheric Brighteningsmentioning

confidence: 66%

Section: Summary and Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A new type of small-scale downflow patches in sunspot penumbrae

Katsukawa

Jurčák

2010

A&A

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“…This scenario has been supported by magnetohydrodynamic simulations (Magara 2010). In particular, Katsukawa & Jurcǎk (2010) and Jurcák & Katsukawa (2010) studied the photospheric response associated with PMJs and found some downflows in the lower photosphere to be related to chromospheric brightenings. They claimed that these could be a possible signature of magnetic reconnection in the middle or low photosphere.…”

Section: Introductionmentioning

confidence: 66%

“…Magnetic reconnection between differently inclined field lines has been suggested as a possible driver of PMJs (e.g., Katsukawa et al 2007;Katsukawa & Jurcǎk 2010;Jurcák & Katsukawa 2010), given that the complex configuration of the magnetic field in sunspot penumbrae involves strong variations of the field strength and inclination over small spatial scales (e.g., Borrero & Ichimoto 2011;Rempel & Schlichenmaier 2011). This scenario has been supported by magnetohydrodynamic simulations (Magara 2010).…”

Section: Introductionmentioning

confidence: 85%

Temporal evolution of short-lived penumbral microjets

Siu-Tapia

Rubio

Suárez

et al. 2020

A&A

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Context. Penumbral microjets (PMJs) is the name given to elongated jet-like brightenings observed in the chromosphere above sunspot penumbrae. They are transient events that last from a few seconds to several minutes, and their origin is presumed to be related to magnetic reconnection processes. Previous studies have mainly focused on their morphological and spectral characteristics, and more recently on their spectropolarimetric signals during the maximum brightness stage. Studies addressing the temporal evolution of PMJs have also been carried out, but they are based on spatial and spectral time variations only. Aims. Here we investigate, for the first time, the temporal evolution of the polarization signals produced by short-lived PMJs (lifetimes < 2 min) to infer how the magnetic field vector evolves in the upper photosphere and mid-chromosphere. Methods. We use fast-cadence spectropolarimetric observations of the Ca II 854.2 nm line taken with the CRisp Imaging Spectropolarimeter at the Swedish 1 m Solar Telescope. The weak-field approximation (WFA) is used to estimate the strength and inclination of the magnetic field vector. By separating the Ca II 854.2 nm line into two different wavelength domains to account for the chromospheric origin of the line core and the photospheric contribution to the wings, we infer the height variation of the magnetic field vector. Results. The WFA reveals larger magnetic field changes in the upper photosphere than in the chromosphere during the PMJ maximum brightness stage. In the photosphere, the magnetic field inclination and strength undergo a transient increase for most PMJs, but in 25% of the cases the field strength decreases during the brightening. In the chromosphere, the magnetic field tends to be slightly stronger during the PMJs. Conclusions. The propagation of compressive perturbation fronts followed by a rarefaction phase in the aftershock region may explain the observed behavior of the magnetic field vector. The fact that such behavior varies among the analyzed PMJs could be a consequence of the limited temporal resolution of the observations and the fast-evolving nature of the PMJs.

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Penumbral Microjets in Sunspot Chromospheres: Evidence of Magnetic Reconnection

Katsukawa

2018

First Ten Years of Hinode Solar on-Orbit Observatory

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Temporal downflows in a penumbra

Cited by 15 publications

References 26 publications

A new type of small-scale downflow patches in sunspot penumbrae

A new type of small-scale downflow patches in sunspot penumbrae

Temporal evolution of short-lived penumbral microjets

Penumbral Microjets in Sunspot Chromospheres: Evidence of Magnetic Reconnection

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