Reappraising Transition Region Line Widths in Light of Recent Alfvén Wave Discoveries

McIntosh, Scott W.; Pontieu, Bart De; Tarbell, T. D.

doi:10.1086/528682

Cited by 35 publications

(38 citation statements)

References 31 publications

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“…Perhaps these are the ones affecting or producing the "straws" or "spicules-II" observed in Ca II H, respectively near the limb by Rutten (2006) and across the limb by De Pontieu et al (2007b), that were interpreted as Alfvén waves by De Pontieu et al (2007c). They may also explain unresolved ultraviolet line broadening (McIntosh et al 2008) and the "rapid blueshift events" at the edge of network concentrations reported by Langangen et al (2008). It is also interesting to note that the higher-temperature regions (i.e.…”

Section: Chromospheric Heatingmentioning

confidence: 98%

The solar chromosphere at high resolution with IBIS

Cauzzi

Reardon

Rutten

et al. 2009

A&A

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The structure and energy balance of the solar chromosphere remain poorly known. We used the imaging spectrometer IBIS at the Dunn Solar Telescope to obtain fast-cadence, multi-wavelength profile sampling of Hα and Ca II 854.2 nm over a sizable two-dimensional field of view encompassing quiet-Sun network. We provide a first inventory of how the quiet chromosphere appears in these two lines by comparing basic profile measurements in the form of image displays, temporal-average displays, time slices, and pixel-by-pixel correlations. We find that the two lines can be markedly dissimilar in their rendering of the chromosphere, but that, nevertheless, both show evidence of chromospheric heating, particularly in and around network: Hα in its core width and Ca II 854.2 nm in its brightness. We discuss venues for improved modeling.

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Section: Chromospheric Heatingmentioning

confidence: 98%

The solar chromosphere at high resolution with IBIS

Cauzzi

Reardon

Rutten

et al. 2009

A&A

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“…From the fits we determine the peak intensity I p , the Doppler shift v D and the 1/e line width σ. The latter is used to determine the non-thermal line broadening σ nt with σ nt = σ 2 − σ 2 th − σ inst where σ th = 6.86 km/s (assuming a formation temperature of 80,000 K, see also McIntosh et al 2008) and σ inst = 3.9 km/s (De Pontieu et al 2014b). …”

Section: Datasetsmentioning

confidence: 99%

Why Is Non-Thermal Line Broadening of Spectral Lines in the Lower Transition Region of the Sun Independent of Spatial Resolution?

Pontieu

McIntosh

Martínez-Sykora

et al. 2015

ApJ

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Spectral observations of the solar transition region (TR) and corona show broadening of spectral lines beyond what is expected from thermal and instrumental broadening. The remaining non-thermal broadening is significant (5-30 km/s) and correlated with the intensity. Here we study spectra of the TR Si IV 1403Å line obtained at high resolution with the Interface Region Imaging Spectrograph (IRIS). We find that the large improvement in spatial resolution (0.33 ) of IRIS compared to previous spectrographs (2 ) does not resolve the non-thermal line broadening which in most regions remains at pre-IRIS levels of about 20 km/s. This invariance to spatial resolution indicates that the processes behind the broadening occur along the line-of-sight (LOS) and/or on spatial scales (perpendicular to the LOS) smaller than 250 km. Both effects appear to play a role. Comparison with IRIS chromospheric observations shows that, in regions where the LOS is more parallel to the field, magneto-acoustic shocks driven from below impact the TR and can lead to significant non-thermal line broadening. This scenario is supported by MHD simulations. While these do not show enough non-thermal line broadening, they do reproduce the long-known puzzling correlation between non-thermal line broadening and intensity. This correlation is caused by the shocks, but only if non-equilibrium ionization is taken into account. In regions where the LOS is more perpendicular to the field, the prevalence of small-scale twist is likely to play a significant role in explaining the invariance and correlation with intensity.

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“…They were found in CA II H near the limb and called 'straws' by Rutten [180], observed as 'type-II spicules' in CA II H off the limb by De Pontieu et al [181,182], and identified on the disc as dark RBEs in the blue wings of Ca II 854.2 nm and Ha by Langangen et al [183] and Rouppe van der Voort et al [184]. They may also be diagnosed from extreme ultraviolet line asymmetries [185][186][187][188][189]. They are probably a key player in providing mass and energy to the corona outside active regions [190].…”

Section: (Iii) Spicules-ii/straws/rapid Blue Excursionsmentioning

confidence: 99%

The quiet-Sun photosphere and chromosphere

Rutten

2012

Phil. Trans. R. Soc. A.

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The overall structure and the fine structure of the solar photosphere outside active regions are largely understood, except possibly the important roles of a turbulent near-surface dynamo at its bottom, internal gravity waves at its top and small-scale vorticity. Classical one-dimensional static radiation-escape modelling has been replaced by three-dimensional time-dependent magento-hydrodynamic simulations that come closer to reality. The solar chromosphere, in contrast, remains little understood, although its pivotal role in coronal mass and energy loading makes it a principal research area. Its fine structure defines its overall structure, so that hard-to-observe and hard-to-model small-scale dynamical processes are key to understanding. However, both chromospheric observation and chromospheric simulation presently mature towards the required sophistication. Open-field features seem of greater interest than easier-to-see closed-field features.

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Reappraising Transition Region Line Widths in Light of Recent Alfvén Wave Discoveries

Cited by 35 publications

References 31 publications

The solar chromosphere at high resolution with IBIS

The solar chromosphere at high resolution with IBIS

Why Is Non-Thermal Line Broadening of Spectral Lines in the Lower Transition Region of the Sun Independent of Spatial Resolution?

The quiet-Sun photosphere and chromosphere

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