Density and Temperature Measurements in a Solar Active Region

Warren, H. P.; Winebarger, Amy R.

doi:10.1086/379094

Cited by 26 publications

(12 citation statements)

References 24 publications

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“…Thus, underdense loops will tend to be hot, and overdense loops cool, as was also noted in a survey of data from TRACE and Yohkoh Soft X-Ray Telescope (SXT) data by Winebarger et al (2003a). This also suggests that the more general overdensity of cooler loops seen by TRACE (e.g., Aschwanden et al 2001;Warren & Winebarger 2003;Winebarger et al 2003a) is a natural consequence of a cyclical heating-cooling of the loops, although verification of this claim in the context of the nanoflare model requires the study of the simultaneous evolution of many strands (see x 3.2).…”

Section: The Evaporation-draining Cycle For a Single Loopmentioning

confidence: 63%

“…Aspects include new results concerning the temperature-emission measure distribution (e.g., Schmelz et al 2001;Schmelz 2002;Martens, Cirtain, & Schmelz 2002;Aschwanden 2002;Warren & Winebarger 2003), the densitytemperature properties of loops (e.g., Reale & Peres 2000;Aschwanden, Schrijver, & Alexander 2001;Testa et al 2002;Warren & Winebarger 2003;Winebarger, Warren, & Mariska 2003a;Winebarger, Warren, & Seaton 2003b), and the suggestion that nanoflare energies are distributed as a power law (see Aschwanden & Parnell 2002 for a summary of the relevant observations). The aim of this paper is to return to our nanoflare model and reinvestigate it in the light of these new issues.…”

Section: Introductionmentioning

confidence: 99%

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Nanoflare Heating of the Corona Revisited

Cargill

Klimchuk

2004

ApJ

186

166

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The radiative signatures of the nanoflare model for coronal heating are investigated. If an observed coronal loop is assumed to consist of many small strands that cannot be distinguished spatially by EUV or X-ray observations, we are able to calculate differential emission-measure profiles and filling factors for a range of heating models. In this picture the strands undergo continual heating and cooling, leading to a corona comprising strands with a broad range of temperatures and densities. Thus, observations over a range of temperatures will show a multithermal coronal structure. The cyclical heating-cooling leads inevitably to loops that are underdense and overdense at high and low temperatures, respectively, compared to what would be expected from static equilibrium models, and in addition, we show that differential emission-measure profiles with shallow slopes can be obtained, as reported in recent observations. The differences between filling factors that can be seen by broadband and narrowband instruments are explored. Loops with broadband filling factors near unity can still have small narrowband factors, and the narrowband factor is shown to be a strong function of the local temperature. Nanoflare energy distributions that are constant, flat, or power laws are considered. Power laws lead to wide distributions of temperatures and densities in the corona, and steep power laws lead to larger filling factors.

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Section: The Evaporation-draining Cycle For a Single Loopmentioning

confidence: 63%

Section: Introductionmentioning

confidence: 99%

Nanoflare Heating of the Corona Revisited

Cargill

Klimchuk

2004

ApJ

186

166

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“…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). They are overdense with respect to hydrostatic equilibrium (Aschwanden et al 2001;Warren & Winebarger 2003), and are better explained by impulsive heating models (e.g., Reale et al 2000;Warren et al 2002). The models rely on chromospheric evaporation to fill the coronal parts of the loop (Antiochos & Sturrock 1978), enhancing the density and the radiative losses.…”

Section: Introductionmentioning

confidence: 99%

Is Active Region Core Variability Age Dependent?

Ugarte-Urra

Warren

2012

ApJ

Self Cite

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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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“…Sterling et al (1999) verified BCS findings by measuring spectral-scans from the Coronal Diagnostic Spectrometer (CDS) on the SOHO, integrated over different heights of an active region. Others have also investigated the thermal structure of active regions with various instruments (e.g., Pye et al 1978;Schadee et al 1983;Watanabe et al 1995;Yoshida & Tsuneta 1996;Warren & Winebarger 2003).…”

Section: Introductionmentioning

confidence: 99%

Hinode extreme-ultraviolet imaging spectrometer observations of a limb active region

O’Dwyer¹,

Zanna²,

Mason³

et al. 2010

A&A

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Aims. We investigate the electron density and temperature structure of a limb active region. Methods. We have carried out a study of an active region close to the solar limb using observations from the Extreme-ultraviolet Imaging Spectrometer (EIS) and the X-ray telescope (XRT) on board Hinode. The electron density and temperature distributions of the coronal emission have been determined using emission line intensity ratios. Differential emission measure (DEM) analysis and the emission measure (EM) loci technique were used to examine the thermal structure of the emitting plasma as a function of distance from the limb. Results. The highest temperature and electron density values are found to be located in the core of the active region, with a peak electron number density value of 1.9 × 10 10 cm −3 measured using the Fe XII 186.887 Å to 192.394 Å line intensity ratio. The plasma along the line of sight in the active region was found to be multi-thermal at different distances from the limb. The EIS and XRT DEM analyses appear to be in agreement in the temperature interval from log T = 6.5−6.7. Conclusions. Our results provide new constraints for models of coronal heating in active regions.

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Density and Temperature Measurements in a Solar Active Region

Cited by 26 publications

References 24 publications

Nanoflare Heating of the Corona Revisited

Nanoflare Heating of the Corona Revisited

Is Active Region Core Variability Age Dependent?

Hinode extreme-ultraviolet imaging spectrometer observations of a limb active region

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