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Brekke, P.

doi:10.1023/a:1005224709046

Cited by 29 publications

(18 citation statements)

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“…Episodes like the strong brightening in the O lines may resemble those analyzed by Chae et al (2000) and interpreted as brightenings (or blinkers, e.g. Brekke 1999).…”

Section: Discussionmentioning

confidence: 90%

CDS/SoHO multi-line observation of a solar active region: Detection of a hot stable loop and of a cool dynamic loop

Giorgio¹,

Reale²,

Peres³

2003

A&A

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Abstract. We analyze a space-, time-and spectral-resolved SoHO/CDS observation of the evolution of an active region over a time lapse of approximately three hours in various spectral lines emitted in the interval of temperature 1.3 × 10 4 < T < 2.5 × 10 6 K. We identify and characterize two structures of interest: a longer coronal loop (≈5.5 × 10 9 cm), relatively steady and well visible in lines forming at coronal temperatures (e.g. Fe XIV 334.17 Å, Fe XVI 360.76 Å) and a smaller one (≈1.8 × 10 9 cm), transient and visible only in cooler lines (O IV 554.51 Å, O V 629.73 Å). In the hot lines, the longer loop has a bright apex and an emission distribution of constant shape, but of moderately variable absolute intensity; the region around the loop apex shows a distinct brightening practically in all lines. In the hot lines, the brightening appears as a minor perturbation over a steadily high emission level. In the same region the emission measure vs temperature of the hottest lines indicates a temperature of ∼2 MK, lower than the temperature obtained from Yohkoh data taken just before the CDS observation. Comparison with steady-state loop scaling laws and with plasma time scales, and connection to cooling or heating episodes are discussed. As for the cool loop, its whole evolution, from ignition to disappearance, is directly observed, confirming the highly transient nature of such structures. The O V line is blue-shifted at one footpoint, indicating an upflow associated with the loop ignition.

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“…Episodes like the strong brightening in the O lines may resemble those analyzed by Chae et al (2000) and interpreted as brightenings (or blinkers, e.g. Brekke 1999).…”

Section: Discussionmentioning

confidence: 90%

CDS/SoHO multi-line observation of a solar active region: Detection of a hot stable loop and of a cool dynamic loop

Giorgio¹,

Reale²,

Peres³

2003

A&A

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“…2.1.4.4). Spectroscopic line ratios obtained by the Coronal Diagnostic Spectrometer (CDS, or SUMER confirm the relatively low temperatures in transition-region loops (Brekke 1999;Chae et al 2000a). The major fraction of the extreme-ultraviolet (EUV) emission in the 8 × 10 4 K to 8 × 10 5 K range, i.e., at transition-region temperatures, stems from small cool loops and other unresolved structures that do not reach coronal temperatures at all .…”

Section: The Thermal Structurementioning

confidence: 83%

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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“…The first timelapse sequences from Skylab revealed that the cooler loops (T 2 MK) have shorter lifetimes, even when not necessarily associated with flare activity (Noyes et al 1975;Levine & Withbroe 1977;Sheeley 1980). Their dynamism, suggestive of a non-steady state (Peres 1997), was confirmed by later missions like Solar and Heliospheric Observatory (SOHO; e.g., Brekke 1999) and Transition Region and Coronal Explorer (Schrijver et al 1999). The loops, which can be found both at the core and the periphery of ARs, evolve on timescales of tens of minutes (e.g., Ugarte-Urra et al 2009;Mulu-Moore et al 2011;Viall & Klimchuk 2011).…”

Section: Introductionmentioning

confidence: 94%

Is Active Region Core Variability Age Dependent?

Ugarte-Urra

Warren

2012

ApJ

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The presence of both steady and transient loops in active region cores has been reported from soft X-ray and extreme-ultraviolet observations of the solar corona. The relationship between the different loop populations, however, remains an open question. We present an investigation of the short-term variability of loops in the core of two active regions in the context of their long-term evolution. We take advantage of the nearly full Sun observations of STEREO and Solar Dynamics Observatory spacecraft to track these active regions as they rotate around the Sun multiple times. We then diagnose the variability of the active region cores at several instances of their lifetime using EIS/Hinode spectral capabilities. We inspect a broad range of temperatures, including for the first time spatially and temporally resolved images of Ca xiv and Ca xv lines. We find that the active region cores become fainter and steadier with time. The significant emission measure at high temperatures that is not correlated with a comparable increase at low temperatures suggests that high-frequency heating is viable. The presence, however, during the early stages, of an enhanced emission measure in the "hot" (3.0-4.5 MK) and "cool" (0.6-0.9 MK) components suggests that low-frequency heating also plays a significant role. Our results explain why there have been recent studies supporting both heating scenarios.

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Cited by 29 publications

References 0 publications

CDS/SoHO multi-line observation of a solar active region: Detection of a hot stable loop and of a cool dynamic loop

CDS/SoHO multi-line observation of a solar active region: Detection of a hot stable loop and of a cool dynamic loop

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

Is Active Region Core Variability Age Dependent?

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