A dynamic model for the solar transition region

Antiochos, S. K.

doi:10.1086/162007

Cited by 32 publications

(15 citation statements)

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“…In order to understand the physics of the Sun's atmosphere from the redshifted and blueshifted emissions, a lot more effort is called for not only from high-resolution spatial and temporal observations but also theoretical modeling. A vast literature exists on the topic from the Skylab era to SOHO and TRACE (e.g., Doschek et al, 1976;Antiochos, 1984; We infer that sunspot plumes are nothing else than the common footpoint of several active region loops, and that the processes are similar to those in normal active region loops. Recent results from a joint observation of the EIS spectrometer on Hinode and the MDI and SUMER instruments on SOHO corroborate this interpretation.…”

Section: Downflows In Ar Loops and Sunspot Plumesmentioning

confidence: 86%

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The redshifted footpoints of coronal loops

et al. 2008

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Abstract. The physics of coronal loops holds the key to understanding coronal heating and the flow of mass and energy in the region. However, the energy source, structure maintenance and mass balance in coronal loops are not yet fully understood. Observations of blue-and redshifted emissions have repeatedly been used in the construction of loop models. But observations and interpretations of line shifts have been widely debated. Here we present detailed SUMER observations, which clearly show a steady downflow in both footpoints of coronal loops observed at transition region (TR) and lower corona temperatures. We also show and quantify a correlation existing between this Doppler shift and the spectral radiance. Our results indicate a strong correlation which holds from the chromosphere to the lower corona. We suggest that the downflow in the footpoints may be a common phenomenon on all scales, which could explain, why on a statistical basis bright pixels tend to be more redshifted. We conclude by presenting interpretation of such results and their implications in the light of a viable coronal loop model. The observation of steady downflow in redshifted footpoints seems to be in conflict with impulsive heating.

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Section: Downflows In Ar Loops and Sunspot Plumesmentioning

confidence: 86%

“…A vast literature exists on the topic from the Skylab era to SOHO and TRACE (e.g., Doschek et al, 1976;Antiochos, 1984;McClymont, 1989;Hansteen, 1993;Brekke, 1993;Antiochos, 1994;Müller et al, 2004;McIntosh and Poland, 2004, and references therein).…”

Section: Introductionmentioning

confidence: 99%

The redshifted footpoints of coronal loops

et al. 2008

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“…How are we to solve this dilemma? Antiochos (1984) proposed a clever explanation. He introduced the concept of a chromospheric 'well' to explain the constancy of redshifts across the disk.…”

Section: Discussionmentioning

confidence: 99%

On Doppler Shift and Its Center-to-limb Variation in Active Regions in the Transition Region

Ghosh

Klimchuk

Tripathi

2019

ApJ

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A comprehensive understanding of the structure of Doppler motions in transition region including the center-to-limb variation and its relationship with the magnetic field structure is vital for the understanding of mass and energy transfer in the solar atmosphere. In this paper, we have performed such a study in an active region using the Si IV 1394Å emission line recorded by the Interface Region Imaging Spectrograph (IRIS) and the line-of-sight photospheric magnetic field obtained by the Helioseismic and Magnetic Imager (HMI) on-board the Solar Dynamics Observatory (SDO). The active region has two opposite polarity strong field regions separated by a weak field corridor, which widened as the active region evolved. On average the strong field regions (corridor) show(s) redshifts of 5-10 (3-9) km s −1 (depending on the date of observation). There is, however, a narrow lane in the middle of the corridor with near-zero Doppler shifts at all disk positions, suggesting that any flows there are very slow. The Doppler velocity distributions in the corridor seem to have two components-a low velocity component centered near 0 km/s and a high velocity component centered near 10 km s −1 . The high velocity component is similar to the velocity distributions in the strong field regions, which have just one component. Both exhibit a small center-to limb variation and seem to come from the same population of flows. To explain these results, we suggest that the emission from the lower transition region comes primarily from warm type II spicules, and we introduce the idea of a 'chromospheric wall'-associated with classical cold spicules-to account for a diminished center-to-limb variation.

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“…In two papers Spadaro et al (1990Spadaro et al ( , 1991 revisited the results of loop models of Antiochos (1984) and Mariska (1988) to reproduce the persistent transition region line shifts and their center-to-limb variation. Especially for the loop model of Mariska (1988) they found the time-dependent ionization resulting in reduced line shifts, even though usually not in a changed sign of the net line shift.…”

Section: Ionization Balancementioning

confidence: 99%

Forward Modeling of the Corona of the Sun and Solar‐like Stars: From a Three‐dimensional Magnetohydrodynamic Model to Synthetic Extreme‐Ultraviolet Spectra

Peter

Gudiksen

Nordlund

2006

ApJ

147

181

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A forward model is described in which we synthesize spectra from an ab initio three-dimensional MHD simulation of an outer stellar atmosphere, where the coronal heating is based on braiding of magnetic flux due to photospheric footpoint motions. We discuss the validity of assumptions such as ionization equilibrium and investigate the applicability of diagnostics like the differential emission measure inversion. We find that the general appearance of the synthesized corona is similar to the solar corona and that, on a statistical basis, integral quantities such as average Doppler shifts or differential emission measures are reproduced remarkably well. The persistent redshifts in the transition region, which have puzzled theorists since their discovery, are explained by this model as caused by the flows induced by the heating through braiding of magnetic flux. While the model corona is only slowly evolving in intensity, as is observed, the amount of structure and variability in Doppler shift is very large. This emphasizes the need for fast coronal spectroscopic observations, as the dynamical response of the corona to the heating process manifests itself in a comparably slow evolving coronal intensity but rapid changes in Doppler shift.

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A dynamic model for the solar transition region

Cited by 32 publications

References 0 publications

The redshifted footpoints of coronal loops

The redshifted footpoints of coronal loops

On Doppler Shift and Its Center-to-limb Variation in Active Regions in the Transition Region

Forward Modeling of the Corona of the Sun and Solar‐like Stars: From a Three‐dimensional Magnetohydrodynamic Model to Synthetic Extreme‐Ultraviolet Spectra

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