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Brekke, P.; Kjeldseth-Moe, O.; Harrison, R. A.

doi:10.1023/a:1004950330900

Cited by 77 publications

(57 citation statements)

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“…Similar discussions on these two broad categories of interpretation (wave model vs. flow model) exist (e.g. Brekke et al 1997).…”

Section: Discussionmentioning

confidence: 69%

“…With the recent operation of more powerful instruments, the list of observational evidence for variability in coronal loops is largely extended. Brekke et al (1997) reported of the first observations of high-velocity flows in active region loop systems observed with the CDS (Coronal Diagnostic Spectrometer) on SoHO. The velocities observed at a temperature of 240 000 K are of the order of 50-60 km s −1 .…”

Section: Introductionmentioning

confidence: 99%

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Slow magnetoacoustic waves in coronal loops: EIT and TRACE

Robbrecht

Verwichte

Berghmans

et al. 2001

A&A

151

113

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Abstract. On May 13, 1998 the EIT (Extreme ultraviolet Imaging Telescope) on board of SoHO (Solar and Heliospheric Observatory) and TRACE (Transition Region And Coronal Explorer) instruments produced simultaneous high cadence image sequences of the same active region (AR 8218). TRACE achieved a 25 s cadence in the Fe ix (171Å) bandpass while EIT achieved a 15 s cadence (operating in "shutterless mode", SoHO JOP 80) in the Fe xii (195Å) bandpass. These high cadence observations in two complementary wavelengths have revealed the existence of weak transient disturbances in an extended coronal loop system. These propagating disturbances (PDs) seem to be a common phenomenon in this part of the active region. The disturbances originate from small scale brightenings at the footpoints of the loops and propagate along the loops. The projected propagation speeds roughly vary between 65 and 150 km s −1 for both instruments which is close to and below the expected sound speed in the coronal loops. The measured slow magnetoacoustic propagation speeds seem to suggest that the transients are sound (or slow) wave disturbances. This work differs from previous studies in the sense that it is based on a multi-wavelength observation of an entire loop bundle at high cadence by two EUV imagers. The observation of sound waves along the same path shows that they propagate along the same loop, suggesting that loops contain sharp temperature gradients and consist of either concentric shells or thin loop threads, at different temperatures.

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“…Similar discussions on these two broad categories of interpretation (wave model vs. flow model) exist (e.g. Brekke et al 1997).…”

Section: Discussionmentioning

confidence: 69%

Section: Introductionmentioning

confidence: 99%

Slow magnetoacoustic waves in coronal loops: EIT and TRACE

Robbrecht

Verwichte

Berghmans

et al. 2001

A&A

151

113

View full text Add to dashboard Cite

show abstract

“…They estimate the accuracy in the line-of-sight velocity determinations to be 5 km s −1 for He I and O V, 10 km s −1 for Mg IX, and 15 km s −1 for O III, O IV, Ne VI and Fe XVI. Brekke et al (1997) analyzed line shifts in active region loops, in particular for O V 629Å, and estimated the uncertainty in the measured shifts to be ≈10 km s −1 . Hence we also do not expect a higher accuracy from the analysis of individual line profiles, in particular due to the low intensity in coronal holes.…”

Section: Discussionmentioning

confidence: 99%

Properties of ultraviolet lines observed with the Coronal Diagnostic Spectrometer (CDS/SOHO) in coronal holes and the quiet Sun

Stucki

Solanki

Pike

et al. 2002

A&A

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Abstract.We present an analysis of 14 ultraviolet emission lines belonging to different atoms and ions observed inside polar coronal holes and in the normal quiet Sun. The observations were made with the Coronal Diagnostic Spectrometer (CDS) onboard the Solar and Heliospheric Observatory (SOHO). This study extends previous investigations made with the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer to higher temperatures. We compare line intensities, shifts and widths in coronal holes with the corresponding values obtained in the quiet Sun. While all lines formed at temperatures above 7 × 10 5 K show clearly the presence of the hole in their intensities, differences in line width are more subtle, with cooler lines being broader in coronal holes, while hotter lines tend to be narrower. According to the present data all lines are blueshifted inside the coronal hole compared to the normal quiet Sun. Almost all the lines formed between 80 000 K and 600 000 K (i.e. transition-region lines) show a correlation between blueshifts and brightness within coronal holes. This is in agreement with the conclusion reached by Hassler et al. (1999) that the fast solar wind emanates from the network and supports our previous study (Stucki et al. 2000b). For coronal lines, this trend seems to be reversed.

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“…In order to avoid confusion, we will refer to them as "intermediate-temperature loops". This class of loops was first studied by Foukal (1976) and observed by Brekke et al (1997). From observations, they are generally detected in the UV lines and appear to be steady for long times even if they are more variable and dynamic than hot coronal loops, probably because of substantial flows (Brekke et al 1997;Di Giorgio et al 2003;Reale 2010).…”

Section: Introductionmentioning

confidence: 94%

Solar low-lying cool loops and their contribution to the transition region EUV output

Sasso

Andretta

Spadaro

et al. 2012

A&A

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Aims. We aim to investigate the increase of the differential emission measure (DEM) towards the chromosphere. In the past 30 years, small and cool magnetic loops (height < ∼ 8 Mm, T < ∼ 10 5 K) have been proposed as an explanation for this effect. Methods. We present hydrodynamic simulations of low-lying cool loops in which we studied the loops' conditions of existence and stability, and their contribution to the transition region EUV output. Results. We find that stable, quasi-static cool loops (with velocities <1 km s −1 ) can be obtained under different and more realistic assumptions on the radiative loss function with respect to previous works. A mixture of the DEMs of these cool loops plus intermediate loops with temperatures between 10 5 and 10 6 K can reproduce the observed emission of the lower transition region at the critical turnup temperature point (T ∼ 2 × 10 5 K) and below T = 10 5 K.

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Cited by 77 publications

References 0 publications

Slow magnetoacoustic waves in coronal loops: EIT and TRACE

Slow magnetoacoustic waves in coronal loops: EIT and TRACE

Properties of ultraviolet lines observed with the Coronal Diagnostic Spectrometer (CDS/SOHO) in coronal holes and the quiet Sun

Solar low-lying cool loops and their contribution to the transition region EUV output

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