Supersonic downflows in the vicinity of a growing pore

Lagg, A.; Woch, J.; Solanki, S. K.; Krupp, N.

doi:10.1051/0004-6361:20054700

Cited by 59 publications

(98 citation statements)

References 47 publications

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“…We then compared their fit quality, which is represented by a "fitness"parameter (see Eqs. (1) and (2) of Lagg et al 2007, for the definition) provided by the Pikaia genetic algorithm (Charbonneau 1995). The two-component model was considered to be necessary only when the quality of the fit, i.e., the fitness parameter, was increased by at least 20% with respect to the one-component fit.…”

Section: Discussionmentioning

confidence: 99%

Magnetic structures of an emerging flux region in the solar photosphere and chromosphere

Lagg²,

Solanki

2010

A&A

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Aims. We investigate the vector magnetic field and Doppler velocity in the photosphere and upper chromosphere of a young emerging flux region of the sun close to disk center. Methods. Spectropolarimetric scans of a young active region made using the second generation Tenerife Infrared Polarimeter (TIP II) on the German Vacuum Tower Telescope (VTT) are analyzed. The scanned area contained multiple sunspots and an emerging flux region. An inversion based on the Milne-Eddington approximation was performed on the full Stokes vector of the chromospheric He I 10 830 Å and the photospheric Si I 10 827.1 Å lines. This provided the magnetic vector and line-of-sight velocity at each spatial point in both atmospheric layers. Results. A clear difference is seen between the complex magnetic structure of the emerging flux region (EFR) in the photosphere and the much simpler structure in the upper chromosphere. The upper chromospheric structure is consistent with a set of emerging loops following elongated dark structures seen in the He I 10 830 Å triplet, similar to arch filament systems (AFS), while in the photosphere we infer the presence of U-loops within the emergence zone. Nonetheless, in general the upper chromospheric field has a similar linear relationship between inclination angle and field strength as the photospheric field: the field is weak (≈300 G) and horizontal in the emergence zone, but strong (up to 850 G) and more vertical near its edges. The field strength decreases from the photosphere to the upper chromosphere by approximately 0.1-0.2 G km −1 (or even less) within the emergence zone and by 0.3-0.6 G km −1 in sunspots located at its edge. We reconstructed the magnetic field in 3D based on the chromospheric vector field under the assumption that the He I 10 830 Å triplet forms along the magnetic field loops. The reconstructed loops are quite flat with supersonic downflows at both footpoints. Arguments and evidence for an enhanced formation height of He I 10 830 Å in arch-filaments seen in this line are provided, which support the validity of the reconstructed loops. Conclusions. The main chromospheric properties of EFRs previously deduced for a single region NOAA 9451 are shown to be valid for another region as well, suggesting that the main original results may have a wider application. The main exception is that only the first region displayed a current sheet in the chromosphere. We propose a scenario in which the relatively complex photospheric structure evolves into the simpler chromospheric one.

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Section: Discussionmentioning

confidence: 99%

Magnetic structures of an emerging flux region in the solar photosphere and chromosphere

Lagg²,

Solanki

2010

A&A

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“…We speculate therefore that some kind of energy-supplying mechanism may act at the footpoints, as photospheric brightenings could suggest (see, e.g., Lagg et al 2007). …”

Section: Discussionmentioning

confidence: 90%

“…Recent investigations on the physical properties of the facular regions around magnetic pores in the solar atmosphere have been carried out by several groups using high-resolution data (Hirzberger 2003;Lagg et al 2007;Giordano et al 2008;Cho et al 2010;Judge et al 2010;Narayan & Scharmer 2010;Vargas Domínguez et al 2010). In this Letter, we report on the evidence for siphon counterflows at the edge of a pore, observed in the solar photosphere by the spectropolarimeter (SP) of the Solar Optical Telescope (SOT; Tsuneta et al 2008) aboard the Hinode satellite (Kosugi et al 2007).…”

Section: Introductionmentioning

confidence: 93%

High-Resolution Observations of Siphon Flows in a Solar Magnetic Pore

Guglielmino

Zuccarello

2011

ApJ

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We investigate signatures of siphon flows in a region around a solar magnetic pore, observed in the photosphere at μ = 0.6, during its decay phase. We analyze high-resolution Stokes spectra acquired by Hinode/Solar Optical Telescope along the Fe i pair at 630.2 nm. We determine the vector magnetic field and the line-of-sight velocity by an inversion of the full Stokes vector using the SIR code. We also analyze photospheric G-band filtergrams. We find evidence of a transient siphon (counter)flow at the edge of the pore. An arch-shaped structure is found to have upflow motions of 4 km s −1 in the footpoint with a stronger magnetic field and positive polarity, and downflows of the same order of magnitude in the footpoint with opposite polarity and a weaker magnetic field. The event is different from those reported in previous observations of the Sun's atmosphere and may represent a physical constraint for numerical models.

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“…It is puzzling, however, that the reports of these events are very sparse, although Parker's scenario should be rather general and occur essentially on an everyday basis for the Sun. Lagg et al (2007) also report high-velocity downflows in He i, but in the vicinity of a growing pore. The downflows were lasting (and increasing) for over an hour, so the convective collapse scenario in this case is rather unlikely.…”

Section: Supersonic Downflowsmentioning

confidence: 80%

The Chromospheric Telescope

Bethge

Peter

Kentischer

et al. 2011

A&A

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Aims. We introduce the Chromospheric Telescope (ChroTel) at the Observatorio del Teide in Izaña on Tenerife as a new multiwavelength imaging telescope for full-disk synoptic observations of the solar chromosphere. We describe the design of the instrument and summarize its performance during the first one and a half years of operation. We present a method to derive line-of-sight velocity maps of the full solar disk from filtergrams taken in and near the He i infrared line at 10 830 Å. Methods. ChroTel observations are conducted using Lyot-type filters for the chromospheric lines of Ca ii K, Hα, and He i 10 830 Å. The instrument operates autonomically and gathers imaging data in all three channels with a cadence of down to one minute. The use of a tunable filter for the He i line allows us to determine line-shifts by calibrating the line-of-sight velocity maps derived from the filtergram intensities with spectrographic data from the Tenerife Infrared Polarimeter at high spatial and spectral resolution. Results. The robotic operation and automated data reduction have proven to operate reliably in the first one and and half years. The achieved spatial resolution of the data is close to the theoretical limit of 2 arcsec in Hα and Ca ii K and 3 arcsec in He i. Line-of-sight velocities in He i can be determined with a precision of better than 3-4 km s −1 when co-temporal spectrographic maps are available for calibration. Conclusions. ChroTel offers a unique combination of imaging in the most important chromospheric lines, along with the possibility to determine line-of-sight velocities in one of the lines. This is of interest for scientific investigations of large-scale structures in the solar chromosphere, as well as for context imaging of high-resolution solar observations.

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Supersonic downflows in the vicinity of a growing pore

Cited by 59 publications

References 47 publications

Magnetic structures of an emerging flux region in the solar photosphere and chromosphere

Magnetic structures of an emerging flux region in the solar photosphere and chromosphere

High-Resolution Observations of Siphon Flows in a Solar Magnetic Pore

The Chromospheric Telescope

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