Slow magnetoacoustic waves in coronal loops: EIT and TRACE

Robbrecht, E.; Verwichte, E.; Berghmans, D.; Hochedez, J.‐F.; Poedts, Stefaan; Nakariakov, V. M.

doi:10.1051/0004-6361:20010226

Cited by 152 publications

(127 citation statements)

References 28 publications

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“…Also, the apparent propagation speed appears constant at these distances. It is consistent with previous observations of this phenomenon, which showed that any noticeable speed variation can appear at larger heights only (Robbrecht et al 2001;Gupta et al 2010). No other periodicities, except 3-min oscillations, are found in the power spectrum of the time signal.…”

Section: The Measurement Of the Apparent Phase Speedsupporting

confidence: 93%

“…The spread of the measured speeds is usually attributed to the variation of the angle between the propagating direction and image plane in different cases. Robbrecht et al (2001) reported that the phase speeds of propagating disturbances measured in TRACE 171 Å (1 MK) are normally lower than those measured in EIT 195 Å (1.6 MK). The temperature-dependence of the phase speed was recently found in polar plumes and the interplume medium with AIA (Krishna Prasad et al 2011).…”

Section: Introductionmentioning

confidence: 88%

“…The follow-up studies (e.g. Ofman et al 1999;De Moortel et al 2000, 2002bRobbrecht et al 2001;King et al 2003;Marsh et al 2003;De Moortel 2009) were carried out with or in combination with the Transition Region and Coronal Explorer (TRACE, see Handy et al 1999), which observed a part of the Sun with a better resolution, 0.5 arcsec/pixel in contrast to the 2.6 arcsec/pixel of SOHO/EIT. The propagating speeds, observed as the apparent speed projected to the image plane perpendicular to the line-of-sight (LOS) of the imagers, were normally found to be lower than the local sound speed (which can be estimated as 152 √ T [MK] ≈ 150−260 km s −1 for the temperature T from 1 MK to 3 MK).…”

Section: Introductionmentioning

confidence: 99%

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Measuring the apparent phase speed of propagating EUV disturbances

Yuan

Nakariakov

2012

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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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Section: The Measurement Of the Apparent Phase Speedsupporting

confidence: 93%

Section: Introductionmentioning

confidence: 88%

Section: Introductionmentioning

confidence: 99%

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Measuring the apparent phase speed of propagating EUV disturbances

Yuan

Nakariakov

2012

A&A

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“…Nakariakov and Ofman (2001) estimated the magnetic field strength in an oscillating loop to be ≈1.3 mT. Slow magnetoacoustic disturbances propagating with speeds of roughly 100 km s −1 have been observed by the EIT and TRACE instruments in active-region loops (Robbrecht et al 2001).…”

Section: Coronal Oscillations and Wavesmentioning

confidence: 99%

Observations of the Sun at Vacuum-Ultraviolet Wavelengths from Space. Part II: Results and Interpretations

et al. 2007

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In Part I of this review, the concepts of solar vacuum-ultraviolet (VUV) observations were outlined together with a discussion of the space instrumentation used for the investigations. A section on spectroradiometry provided some quantitative results on the solar VUV radiation without considering any details of the solar phenomena leading to the radiation. Here, in Part II, we present solar VUV observations over the last decades and their interpretations in terms of the plasma processes and the parameters of the solar atmosphere, with emphasis on the spatial and thermal structures of the chromosphere, transition region and corona of the quiet Sun. In addition, observations of active regions, solar flares and prominences are included as well as of small-scale events. Special sections are devoted to the elemental composition of the solar atmosphere and theoretical considerations on the heating of the corona and the generation of the solar wind.

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“…Doschek et al (2008) also used EIS observations to investigate strong blueshifts at the periphery of an AR, which might contribute significantly to the solar wind. On the other hand, the propagation of an intensity disturbance may be explained as a slow magnetoacoustic wave, since the inferred speed is close to or below the coronal sound speed (Robbrecht et al 2001). But the phase speed reported in Robbrecht et al (2001) is the projected speed component rather than the true phase speed, which may exceed the coronal sound speed.…”

Section: Introductionmentioning

confidence: 98%

Intermittent outflows at the edge of an active region – a possible source of the solar wind?

He¹,

Marsch²,

Tu³

et al. 2010

A&A

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Context. It has already been established that the solar wind may originate at the edges of active regions (ARs), but the key questions of how frequently these outflows occur, and at which height the nascent solar wind originates have not yet been addressed. Aims. We study the occurrence rate of these intermittent outflows, the related plasma activities beneath in the low solar atmosphere, and the interplanetary counterparts of the nascent solar wind outflow. Methods. We use the observations from XRT/Hinode and TRACE to study the outflow patterns. The occurrence frequency of the intermittent outflow is estimated by counting the occurrences of propagating intensity enhancements in height-time diagrams. We adopt observations of SOT/Hinode and EIS/Hinode to investigate the phenomena in the chromosphere associated with the coronal outflows. The ACE plasma and field in-situ measurements near Earth are used to study the interplanetary manifestations. Results. We find that in one elongated coronal emission structure, referred to as strand, the plasma flows outward intermittently, about every 20 min. The flow speed sometimes exceeds 200 km s −1 , which is indicative of rapid acceleration, and thus exceeds the coronal sound speed at low altitudes. The inferred flow speed of the soft-X-ray-emitting plasma component seems a little higher than that of the Fe ix/x-emitting plasma component. Chromospheric jets are found to occur at the root of the strand. Upflows in the chromosphere are also confirmed by blue-shifts of the He ii line. The heliospheric plasma counterpart close to the Earth is found to be an intermediate-speed solar wind stream. The AR edge may also deliver some plasmas to a fraction of the fast solar wind stream, most of which emanate from the neighboring CH. Conclusions. The possible origin of the nascent solar wind in the chromosphere, the observed excessive outflow speed of over 200 km s −1 in the lower corona, and the corresponding intermediate-speed solar wind stream in interplanetary space are all linked in our case study. These phenomena from the low solar atmosphere to the heliosphere near Earth in combination shed new light on the solar wind formation process. These observational results will constrain future modeling of the solar winds originating close to an AR.

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Slow magnetoacoustic waves in coronal loops: EIT and TRACE

Cited by 152 publications

References 28 publications

Measuring the apparent phase speed of propagating EUV disturbances

Measuring the apparent phase speed of propagating EUV disturbances

Observations of the Sun at Vacuum-Ultraviolet Wavelengths from Space. Part II: Results and Interpretations

Intermittent outflows at the edge of an active region – a possible source of the solar wind?

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