Sizes of quiet Sun transition region structures

Gontikakis, C.; Peter, Hardi; Dara, H. C.

doi:10.1051/0004-6361:20030940

Cited by 16 publications

(15 citation statements)

References 39 publications

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“…Therefore, we did not study the images of the shift and width of this line. Figure 3 demonstrates that the intensity size is larger than that associated with the Doppler shift and non-thermal width, a result has been found before by Gontikakis et al (2003). It could be due to the orientation of the magnetic field, since the observed Doppler shift and non-thermal motion correspond to the line-of-sight components, which are expected to be large only in the vertical legs of magnetic loops.…”

Section: Resultssupporting

confidence: 56%

“…We first calculated the 2-D ACF of each image by shifting it in both dimensions, and then took its angular average in rings of integer radius and derived a curve of the correlation coefficient against radial distance (Patsourakos et al 1999). The HWHM of the ACF is considered to be the scale size of the feature, while the distance between the primary and secondary peak corresponds to the mean distance between two adjacent features (Patsourakos et al 1999;Gontikakis et al 2003;Ravindra & Venkatakrishnan 2003). Here we are only interested in the HWHM.…”

Section: Resultsmentioning

confidence: 99%

“…Here we are only interested in the HWHM. The smaller the features, the sharper the central peak of the ACF will be (Gontikakis et al 2003).…”

Section: Resultsmentioning

confidence: 99%

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Sizes of transition-region structures in coronal holes and in the quiet Sun

Marsch¹,

Tu²,

Xia³

et al. 2008

A&A

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Aims. We study the height variations of the sizes of chromospheric and transition-region features in a small coronal hole and the adjacent quiet Sun, considering images of the intensity, Doppler shift, and non-thermal motion of ultraviolet emission lines as measured by SUMER (Solar Ultraviolet Measurements by Emitted Radiation), together with the magnetic field as obtained by extrapolation from photospheric magnetograms. Methods. In order to estimate the characteristic sizes of the different features present in the chromosphere and transition region, we have calculated the autocorrelation function for the images as well as the corresponding extrapolated magnetic field at different heights. The Half Width at Half Maximum (HWHM) of the autocorrelation function is considered to be the characteristic size of the feature shown in the corresponding image. Results. Our results indicate that, in both the coronal hole and quiet Sun, the HWHM of the intensity image is larger than that of the images of Doppler-shift and non-thermal width at any given altitude. The HWHM of the intensity image is smaller in the chromosphere than in the transition region, where the sizes of intensity features of lines at different temperatures are almost the same. But in the upper part of the transition region, the intensity size increases more strongly with temperature in the coronal hole than in the quiet Sun. We also studied the height variations of the HWHM of the magnetic field magnitude B and its component |B z |, and found they are equal to each other at a certain height below 40 Mm in the coronal hole. The height variations of the HWHM of |B z /B| seem to be consistent with the temperature variations of the intensity size. Conclusions. Our results suggest that coronal loops are much lower, and magnetic structures expand through the upper transition region and lower corona much more strongly with height in the coronal hole than in the quiet Sun.

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Section: Resultssupporting

confidence: 56%

Section: Resultsmentioning

confidence: 99%

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Sizes of transition-region structures in coronal holes and in the quiet Sun

Marsch¹,

Tu²,

Xia³

et al. 2008

A&A

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“…In this paper, we will concentrate on the Doppler shift of Ne viii. This data set has been intensively studied before by Dammasch et al (1999), Hassler et al (1999), Peter (2000), Gontikakis et al (2003), Tu et al (2005b), and He et al (2007). More details about the observations can be found in these papers.…”

Section: Data Analysis and Resultsmentioning

confidence: 99%

Signature of mass supply to quiet coronal loops

Tian¹,

Tu²,

Marsch³

et al. 2007

A&A

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Aims. The physical implication of large blue shift of Ne viii in the quiet Sun region is investigated in this paper. Methods. We compare the significant Ne viii blue shifts, which are visible as large blue patches on the Doppler-shift map of a middlelatitude quiet-Sun region observed by SUMER, with the coronal magnetic-field structures as reconstructed from a simultaneous photospheric magnetogram by means of a force-free-field extrapolation. Results. We show for the first time that coronal funnels also exist in the quiet Sun. The region studied contains several small funnels that originate from network lanes, expand with height and finally merge into a single wide open-field region. However, the large blue shifts of the Ne viii line are not generally associated with funnels. A comparison between the projections of coronal loops onto the solar x−y-plane and the Ne viii dopplergram indicates that there are some loops that reveal large Ne viii blue shifts in both legs, and some loops with upflow in one and downflow in the other leg.Conclusions. Our results suggest that strong plasma outflow, which can be traced by large Ne viii blue shift, is not necessarily associated with the solar wind originating in coronal funnels but appears to be a signature of mass supply to coronal loops. Under the assumption that the measured Doppler shift of the Ne viii line represents the real outflow velocity of the neon ions being markers of the proton flow, we estimate the mass supply rate to coronal loops to be about 10 34 s −1 .

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“…The network cell has a size of Article published by EDP Sciences 20 000-30 000 km (Simon & Leighton 1964), and lasts for 20 to 50 h (Simon & Leighton 1964;Schrijver 1997;Raju et al 1998). The height variation in the network size can be found in Patsourakos et al (1999), Gontikakis et al (2003), and Tian et al (2008b). Gabriel (1976) proposed the first magnetic network model, in which the transition region emission originates from funnels diverging with height from the underlying supergranular boundary.…”

Section: Introductionmentioning

confidence: 99%

Radiance and Doppler shift distributions across the network of the quiet Sun

Xia

2008

A&A

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Aims. The radiance and Doppler-shift distributions across the solar network provide observational constraints of two-dimensional modeling of transition-region emission and flows in coronal funnels. These distributions have not, however, been studied in detail and we attempt an investigation for a quiet Sun region. Methods. Two different methods, dispersion plots and average-profile studies, were applied to investigate these distributions for three EUV lines. In the dispersion plots, we divided the entire quiet Sun region scanned by SUMER into a bright and a dark part according to an image of Fe xii taken by EIT during the scanning; we plotted intensities and Doppler shifts in each bin as determined according to a filtered intensity of Si ii. We also studied the difference in height variations of the magnetic field as extrapolated from the MDI magnetogram, in and outside network, in the two parts. For the average-profile study, we selected 74 individual cases and derived the average profiles of intensities and Doppler shifts across the network. Cases with large values of blue shift of Ne viii were further studied.Results. The dispersion plots reveal that the intensities of Si ii and C iv increase from network boundary to network center in both the bright and dark parts. However, the intensity of Ne viii shows different trends, namely increasing in the bright part and decreasing in the dark part. In both parts, the Doppler shift of C iv increases steadily from internetwork to network center. The height variations in the magnetic field imply a more homogeneous magnetic structure at greater heights and clearly reflect the different magnetic structures in the two regions. The average-profile study reveals that the intensities of the three lines all decline from the network center to internetwork region. The binned intensities of Si ii and Ne viii have a good correlation. We also find that the large blue shift of Ne viii does not coincide with large red shift of C iv. Conclusions. Our results suggest that the network structure is still prominent at the layer where Ne viii is formed in the quiet Sun, and that the magnetic structures expand more strongly in the dark part than in the bright part of this quiet Sun region. Our results might also hint for a scenario of magnetic reconnection between open funnels and side loops.

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Sizes of quiet Sun transition region structures

Cited by 16 publications

References 39 publications

Sizes of transition-region structures in coronal holes and in the quiet Sun

Sizes of transition-region structures in coronal holes and in the quiet Sun

Signature of mass supply to quiet coronal loops

Radiance and Doppler shift distributions across the network of the quiet Sun

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