Post-flare loops of 26 June 1992

Wiik, J. E.; Schmieder, B.; Heinzel, P.; Roudier, Th.

doi:10.1007/bf00179357

Cited by 28 publications

(27 citation statements)

References 3 publications

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“…This effect is seen earlier in almost all speed analyses of plasma blobs coming down along solar flare loops (Wiik et al 1996;Heinzel et al 1992;Loughhead & Bray 1984), see e.g. the results found by Wiik et al (1996) in Fig.…”

Section: Interpretation Of Intensity Variations and Speedssupporting

confidence: 63%

“…In order to analyze the downward motions in further detail, we follow the method used by Wiik et al (1996) in their analysis of intensity variations along off-limb loops in Hα. The loops in Wiik et al are definitely related to a flare, i.e.…”

Section: Detailed Analysis Of Intensity Variationsmentioning

confidence: 99%

“…11. Wiik et al (1996): flow velocities along a flare loop leg of 100 Mm. The asterisks in the plot are computed from Doppler velocities using three slightly different shape models of the loop; the other symbols represent the velocities derived from the displacements of the blobs.…”

Section: Interpretation Of Intensity Variations and Speedsmentioning

confidence: 99%

“…It is clear from the plot that they found a very similar departure from the free-fall velocity in the lower part of the loop. As reviewed by Wiik et al (1996), several explanations for such plasma deceleration are proposed by different authors. Since for flare loops the gas pressure gradients of the cool gas seem to be insufficient to decelerate fast moving plasma (Heinzel et al 1992), Loughhead & Bray (1984) and Heinzel et al (1992) suggested three other possible explanations: a global variation of the loop's magnetic structure during the typical fall-time of the blobs, deceleration by a presumed helicity of the magnetic field inside the loops, and deceleration of cool blobs as they move inside a hotter plasma.…”

Section: Interpretation Of Intensity Variations and Speedsmentioning

confidence: 99%

“…Most observations are taken in chromospheric lines like the Ca -line and Hα (e.g. Loughhead & Bray 1984;Delone et al 1989;Heinzel et al 1992;Wiik et al 1996). Since the loops are usually only partly filled with Hα-or Ca -emitting material, the fine structure revealed by high spatial resolution observations consists of bright blobs moving downwards which are often almost equidistant leading to terms like "train of blobs".…”

Section: Introductionmentioning

confidence: 99%

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Intensity variations in EIT shutterless mode: Waves or flows?

Groof

Berghmans²,

Driel-Gesztelyi

et al. 2004

A&A

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Abstract. On 11 July 2001 an EIT shutterless campaign was conducted which provided 120 high-cadence (68 s) 304 Å images of the north eastern quarter of the Sun. The most interesting feature seen in the data is an off-limb half loop structure along which systematic intensity variations are seen which appear to propagate from the top of the loop towards its footpoint. We investigate the underlying cause of these propagating disturbances, i.e. whether they are caused by waves or by plasma flows. First we identify 7 blobs with the highest intensities and follow them along the loop. By means of a location-time plot, bulk velocities can be measured at several locations along the loop. The velocity curve found this way is then compared with characteristic wave speeds and with the free-fall speed in order to deduce the nature of the intensity variations. Additional information on density and temperature is derived by measuring the relative intensity enhancements and comparing the EIT 304 Å sequence with Big Bear data and 171 Å data (TRACE/EIT). The combination of all these constraints gives us an insight on the nature and origin of these intensity variations. The idea of slow magneto-acoustic waves is rejected, and we find several arguments supporting that these intensity variations are due to flowing/falling plasma blobs.

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Section: Interpretation Of Intensity Variations and Speedssupporting

confidence: 63%

Section: Detailed Analysis Of Intensity Variationsmentioning

confidence: 99%

Section: Interpretation Of Intensity Variations and Speedsmentioning

confidence: 99%

Section: Interpretation Of Intensity Variations and Speedsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Intensity variations in EIT shutterless mode: Waves or flows?

Groof

Berghmans²,

Driel-Gesztelyi

et al. 2004

A&A

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Post-Flare Loops in the Chromosphere and Corona

Driel‐Gesztelyi

Wiik

Schmieder³

1997

Theoretical and Observational Problems Related to Solar Eclipses

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Post-flare loops of 26 June 1992

et al. 1996

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We observed the large post-flare loop system, which developed after the X 3.9 flare of 25 June 1992 at 20:11 UT, in Hoe with the Multichannel Subtractive Double Pass Spectrograph at Pic-du-Midi and in X-rays with the it Yohkoh/SXT instrument. Following the long-term development of cool and hot plasmas, we have determined the emission measure of the cool plasma and, for the first time, the temporal evolution of the hot-loop emission measure and temperature during the entire gradual phase. Thus, it was possible to infer the temporal variation of electron densities, leading to estimates of cooling times. A gradual decrease of the hot-loop emission measure was observed, from 4 x 1030 cm -5 at 23:00 UT on 25 June 1992 to 3 x 102s cm -5 at 13:10 LIT on 26 June 1992. During the same period, the temperature decreased only slowly from 7.2 to 6.0 x 106 K. Using recent results of NLTE modeling of prominence-like plasmas, we also derive the emission measure of cool Hc~ loops and discuss their temperature and ionisation degree. During two hours of Hoe observations (11-13 hours after the flare) the averaged emission measure does not show any significant change, though the amount of visible cool material decreases and the volume of the loops increases. The emission measure in Hc~, after correction for the Doppler-brightening effect, is slightly lower than in soft X-rays. Since the hot plasma seems to be more spatially extended, we arrive at electron densities hot cool 10 3 in the range n~ _< n~ ~ 2 x 10 cm-at the time of the Hc~ observations. These results are consistent with the post-flare loop model proposed by Forbes, Malherbe, and Priest (1989). The observed slow decrease of the emission measure could be due to an increase of the volume of the loops and a gradual decrease of the chromospheric ablation driven by the reconnection, which seems to remain effective continuously for more than 16 hours. The cooling time for hot loops to cool down to 104 K and to appear in Hoe would be only a few minutes at the beginning of the gradual phase but could be as long as 2 hours at the end, several hours later.

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Post-flare loops of 26 June 1992

Cited by 28 publications

References 3 publications

Intensity variations in EIT shutterless mode: Waves or flows?

Intensity variations in EIT shutterless mode: Waves or flows?

Post-Flare Loops in the Chromosphere and Corona

Post-flare loops of 26 June 1992

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