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

Wilhelm, K.; Marsch, E.; Dwivedi, B. N.; Feldman, U.

doi:10.1007/s11214-007-9285-0

Cited by 41 publications

(37 citation statements)

References 590 publications

(556 reference statements)

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“…Improvements were obtained later in the SOHO mission with increased interest in this line. New solutions for the operation modes were found, allowing access to the full line profile (e.g., Wilhelm et al, 1995Wilhelm et al, , 2004Wilhelm et al, , 2007Ebadi et al, 2009;Curdt and Tian, 2010).…”

Section: Prominence Observations Todaymentioning

confidence: 99%

Solar Prominences: Observations

Parenti

2014

Living Rev. Solar Phys.

290

234

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Solar prominences are one of the most common features of the solar atmosphere. They are found in the corona but they are one hundred times cooler and denser than the coronal material, indicating that they are thermally and pressure isolated from the surrounding environment. Because of these properties they appear at the limb as bright features when observed in the optical or the EUV cool lines. On the disk they appear darker than their background, indicating the presence of a plasma absorption process (in this case they are called filaments). Prominence plasma is embedded in a magnetic environment that lies above magnetic inversion lines, denoted a filament channel.This paper aims at providing the reader with the main elements that characterize these peculiar structures, the prominences and their environment, as deduced from observations. The aim is also to point out and discuss open questions on prominence existence, stability and disappearance.The review starts with a general introduction of these features and the instruments used for their observation. Section 2 presents the large scale properties, including filament morphology, thermodynamical parameters, magnetic fields, and the properties of the surrounding coronal cavity, all in stable conditions. Section 3 is dedicated to small-scale observational properties, from both the morphological and dynamical points of view. Section 4 introduces observational aspects during prominence formation, while Section 5 reviews the sources of instability leading to prominence disappearance or eruption. Conclusions and perspectives are given in Section 6.

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Section: Prominence Observations Todaymentioning

confidence: 99%

Solar Prominences: Observations

Parenti

2014

Living Rev. Solar Phys.

290

234

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“…However, until recently it was difficult to identify directly the properties of Alfvén waves in the solar atmosphere from optical observations. An indirect piece of evidence of the existence of Alfvén waves or turbulence is the extraordinary, besides the thermal motion effect, Doppler broadening of emission lines when observed on the disk (see the review by Wilhelm et al 2007) and off the solar limb (e.g., Tu et al 1998). The existence of Alfvén waves in the coronal plasma has been recently reported by Tomczyk et al (2007), a result which is based on crosscorrelation analysis of Fe xiii (1074.7 nm) Line-of-Sight (LOS) Doppler velocity time series.…”

Section: Introductionmentioning

confidence: 99%

Upward propagating high-frequency Alfvén waves as identified from dynamic wave-like spicules observed by SOT onHinode

Marsch³

et al. 2009

A&A

102

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Aims. We identify high-frequency Alfvén waves propagating upward in the solar chromosphere and transition region from observation by Solar Optical Telescope (SOT) onboard Hinode. Methods. The spicule shape is enhanced through application of a normal radial gradient filter and an un-sharp mask on the images taken by SOT. The displaced position of the spicule is at each height obtained by tracing the maximum intensity after image processing. The dominant wave period is obtained by the FFT method applied to the time variations of the displaced position at a certain height. The phase speed is estimated with the help of a cross-correlation analysis of two temporal sequences of the displaced positions at two heights along the spicule. Results. We find in four cases that the spicules are modulated by high-frequency (≥0.02 Hz) transverse fluctuations. Such fluctuations are suggested to be Alfvén waves that propagate upward along the spicules with phase speed ranges from 50 to 150 km s −1 . Three of the modulated spicules show clear wave-like shapes with short wavelengths less than 8 Mm. Conclusions. Our work identified directly upward propagation of Alfvén waves in the solar chromosphere and transition region. In addition to the recently reported Alfvén waves with very long wavelength and wave period, we find here four examples of Alfvén waves with shorter wavelengths and periods. These findings shed new light on the wave origin and on coronal and solar-wind heating.

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“…Unfortunately, the coronal plasma is not directly accessible but only remotely via ultraviolet imaging and spectroscopy (see, e.g., the comprehensive reviews by Wilhelm et al 2004Wilhelm et al , 2007. The corresponding observations generally show line intensity fluctuations and Doppler shifts indicative of plasma flows and wave motions.…”

Section: Introductionmentioning

confidence: 99%

A novel technique to measure intensity fluctuations in EUV images and to detect coronal sound waves nearby active regions

Stenborg

Marsch

Vourlidas

et al. 2010

A&A

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Context. In the past years, evidence for the existence of outward-moving (Doppler blue-shifted) plasma and slow-mode magnetoacoustic propagating waves in various magnetic field structures (loops in particular) in the solar corona has been found in ultraviolet images and spectra. Yet their origin and possible connection to and importance for the mass and energy supply to the corona and solar wind is still unclear. There has been increasing interest in this problem thanks to the high-resolution observations available from the extreme ultraviolet (EUV) imagers on the Solar TErrestrial RElationships Observatory (STEREO) and the EUV spectrometer on the Hinode mission. Aims. Flows and waves exist in the corona, and their signatures appear in EUV imaging observations but are extremely difficult to analyse quantitatively because of their weak intensity. Hence, such information is currently available mostly from spectroscopic observations that are restricted in their spatial and temporal coverage. To understand the nature and origin of these fluctuations, imaging observations are essential. Here, we present measurements of the speed of intensity fluctuations observed along apparently open field lines with the Extreme UltraViolet Imagers (EUVI) onboard the STEREO mission. One aim of our paper is to demonstrate that we can make reliable kinematic measurements from these EUV images, thereby complementing and extending the spectroscopic measurements and opening up the full corona for such an analysis. Another aim is to examine the assumptions that lead to flow versus wave interpretation for these fluctuations. Methods. We have developed a novel image-processing method by fusing well established techniques for the kinematic analysis of coronal mass ejections (CME) with standard wavelet analysis. The power of our method lies with its ability to recover weak intensity fluctuations along individual magnetic structures at any orientation, anywhere within the full solar disk, and using standard synoptic observing sequences (cadence <3 min) without the need for special observation plans. Results. Using information from both EUVI imagers, we obtained wave phase speeds with values on the order of 60−90 km s −1 , compatible with those obtained by other previous measurements. Moreover, we studied the periodicity of the observed fluctuations and established a predominance of a 16-min period, and other periods that seem to be multiples of an underlying 8-min period. Conclusions. The validation of our analysis technique opens up new possibilities for the study of coronal flows and waves, by extending it to the full disk and to a larger number of coronal structures than has been possible previously. It opens up a new scientific capability for the EUV observations from the recently launched Solar Dynamics Observatory. Here we clearly establish the ubiquitous existence of sound waves which continuously propagate along apparently open magnetic field lines.

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

Cited by 41 publications

References 590 publications

Solar Prominences: Observations

Solar Prominences: Observations

Upward propagating high-frequency Alfvén waves as identified from dynamic wave-like spicules observed by SOT onHinode

A novel technique to measure intensity fluctuations in EUV images and to detect coronal sound waves nearby active regions

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