Nonthermal Velocities in Solar Active Regions Observed with the Extreme-Ultraviolet Imaging Spectrometer on
                    <i>Hinode</i>

Doschek, G. A.; Mariska, J. T.; Warren, H. P.; Brown, C. M.; Culhane, J. L.; Hara, Hirohisa; Watanabe, Tetsuya; Young, Peter R.; Mason, H. E.

doi:10.1086/522087

Cited by 102 publications

(92 citation statements)

References 11 publications

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“…In the light of the most recent observations, it seems fundamental to study, both theoretically and numerically, the impact of small-scale phenomena on the coronal heating. Note that the most recent Hinode pictures seem to show a magnetic field controlled by plasma turbulence at all scales in which Alfvén waves are omnipresent (see e.g., Doschek et al, 2007;Nishizuka et al, 2008). Thus, the turbulent activity of the corona is one of the key issues to understand the heating processes.…”

Section: Heating Of the Solar Coronamentioning

confidence: 99%

Wave turbulence in magnetized plasmas

Galtier

2009

Nonlin. Processes Geophys.

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Abstract. The paper reviews the recent progress on wave turbulence for magnetized plasmas (MHD, Hall MHD and electron MHD) in the incompressible and compressible cases. The emphasis is made on homogeneous and anisotropic turbulence which usually provides the best theoretical framework to investigate space and laboratory plasmas. The solar wind and the coronal heating problems are presented as two examples of application of anisotropic wave turbulence. The most important results of wave turbulence are reported and discussed in the context of natural and simulated magnetized plasmas. Important issues and possible spurious interpretations are also discussed.

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Section: Heating Of the Solar Coronamentioning

confidence: 99%

Wave turbulence in magnetized plasmas

Galtier

2009

Nonlin. Processes Geophys.

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“…Doschek et al 2007Doschek et al , 2008Sakao et al 2007;Del Zanna 2008;Harra et al 2008;Hara et al 2008;De Pontieu & McIntosh 2010;Tian et al 2011a,b;Martínez-Sykora et al 2011). A single Gaussian fit to the spectral lines suggest that the flow speed is about ∼10 km s −1 , much less than the observed apparent speed of propagating disturbances.…”

Section: Introductionmentioning

confidence: 96%

Measuring the apparent phase speed of propagating EUV disturbances

Yuan

Nakariakov

2012

A&A

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Context. Propagating disturbances of the EUV emission intensity are commonly observed over a variety of coronal structures. Parameters of these disturbances, particularly the observed apparent (image-plane projected) propagation speed, are important tools for MHD coronal seismology. Aims. We design and test tools to reliably measure the apparent phase speed of propagating disturbances in imaging data sets. Methods. We designed cross-fitting technique (CFT), 2D coupled fitting (DCF) and best similarity match (BSM) to measure the apparent phase speed of propagating EUV disturbances in the running differences of time-distance plots (R) and background-removed and normalised time-distance plots (D).Results. The methods were applied to the analysis of quasi-periodic EUV disturbances propagating at a coronal fan-structure of active region NOAA11330 on 27 Oct. 2011, observed with the Atmospheric Imaging Assembly (AIA) on SDO in the 171 Å bandpass. The noise propagation in the AIA image processing was estimated, resulting in the preliminary estimation of the uncertainties in the AIA image flux. This information was used in measuring the apparent phase speed of the propagating disturbances with the CFT, DCF and BSM methods, which gave consistent results. The average projected speed is measured at 47.6 ± 0.6 km s −1 and 49.0 ± 0.7 km s −1 for R and D, with the corresponding periods at 179.7 ± 0.2 s and 179.7 ± 0.3 s, respectively. We analysed the effects of the lag time and the detrending time in the running difference processing and the background-removed plot, on the measurement of the speed, and found that they are fairly weak. Conclusions. The CFT, DCF and BSM methods are found to be reliable techniques for measuring the apparent (projected) phase speed. The samples of larger effective spatial length are more suitable for these methods. Time-distance plots with background removal and normalisation allow for more robust measurements, with little effect of the choice of the detrending time. Cross-fitting technique provides reliable measurements on good samples (e.g. samples with large effective detection length and recurring features). 2D coupled-fitting is found to be sensitive to the initial guess for parameters of the 2D fitting function. Thus DCF is only optimised in measuring one of the parameters (the phase speed in our application), while the period is poorly measured. Best similarity measure is robust for all types of samples and very tolerant to image pre-processing and regularisation (smoothing).

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“…Thus, when analyzing the spectroscopic data, we need to focus on physical conditions of plasma, such as flows and shocks. In addition, non-thermal velocities measured as an excess of line thermal broadening are thought to be caused by turbulence, waves, or velocity gradients; those velocities provide important information for examining the coronal heating mechanism [7]. Doscheck et al [7] and Imada et al [8] estimated non-thermal velocities in the solar active region by using Fe XII and Fe XVI lines, and obtained values of 30 -60 km s −1 and approximately 13 km s −1 , respectively.…”

Section: Introductionmentioning

confidence: 99%

Validation of Spectroscopic Model for Fe Ions in Non-Equilibrium Ionization Plasma in LHD and Hinode

Murakami

Watanabe

Suzuki

et al. 2014

Plasma and Fusion Research

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We measured extreme ultraviolet spectra of Fe ions for plasmas produced in the Large Helical Device (LHD) at the National Institute for Fusion Science (NIFS). Iron was injected into the plasmas by using a tracerencapsulated pellet. By controlling the neutral beam injection pattern, we could produce plasma with a central electron temperature of approximately 500 eV, which was suitable for producing Fe XVII ions. We measured seven Fe XVII lines. The intensity ratio for λ of 20.468 to 25.493 nm was consistent with the theoretically calculated value of 1.1. This calculated value was determined purely from the branching ratio due to the common upper level of these transitions, although Warren et al. [Astrphys. J. 685, 1277(2008] reported a larger ratio of approxinately 2 from Hinode EIS measurements. The other five ratios for Fe XVII lines in our LHD measurements were also consistent with the theoretical ratios calculated with a collisional-radiative model. A preferred atomic dataset for Fe XVII is suggested to obtain better agreement between the measured and calculated ratios.

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Nonthermal Velocities in Solar Active Regions Observed with the Extreme-Ultraviolet Imaging Spectrometer on Hinode

Cited by 102 publications

References 11 publications

Wave turbulence in magnetized plasmas

Wave turbulence in magnetized plasmas

Measuring the apparent phase speed of propagating EUV disturbances

Validation of Spectroscopic Model for Fe Ions in Non-Equilibrium Ionization Plasma in LHD and Hinode

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