Evidence for Nonuniform Heating of Coronal Loops Inferred from Multithread Modeling of<i>TRACE</i>Data

Aschwanden, Markus J.; Nightingale, R. W.; Alexander, David

doi:10.1086/309486

Cited by 265 publications

(223 citation statements)

References 38 publications

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“…Taking into account microwave polarization observations, longitudinal magnetic fields of 3 mT to 6 mT were deduced for heights between 5 Mm and 10 Mm in the corona (Brosius et al 1993(Brosius et al , 1996. Compared to theoretical expectations for static, uniformly heated loops, TRACE observations indicated that many active-region loops have much higher radiances, and presumably higher electron densities (Lenz et al 1999;Aschwanden et al 2000bAschwanden et al , 2001a. They are referred to as "overdense" loops, because the observed density is in excess of that predicted by scaling laws.…”

Section: Active Regionsmentioning

confidence: 97%

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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Section: Active Regionsmentioning

confidence: 97%

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

et al. 2007

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“…Recent results have also shown that simple scaling laws may not be universally applicable, not holding for some loop classes such as cool transition region loops (Oluseyi et al 1999a(Oluseyi et al , 1999b or Ñaring loops (Garcia 1998), while and Aschwanden, Nightengale, & Alexander (2000a) have also highlighted inconsistencies associated with scaling law relationships. The EUV instruments on board SOHO and particularly T RACE have further added to our ability to measure coronal plasma properties in addition to studying the morphology of solar features, a fact that is clearly highlighted in Aschwanden et al (1999Aschwanden et al ( , 2000aAschwanden et al ( , 2000b. Unfortunately, instruments such as SXT and EIT form images through narrowband Ðlters that can under certain conditions include contributions from plasmas with di †er-ing temperatures.…”

Section: Introductionmentioning

confidence: 99%

“…Imaging spectrometers, apart from allowing the study of spectrally pure images, also allow us to measure detailed plasma properties such as electron temperature, density, and bulk plasma motions. Several excellent examples of EUV and X-ray imaging and spectroscopy of active regions can be found in the following : Solar EUV Rocket Telescope and Spectrograph (SERTS) in Brosius et al (1996Brosius et al ( , 1997a, Y ohkoh in Sterling et al (1997Sterling et al ( , 1999, CDS in Fludra et al (1997) and , and T RACE in Schrijver et al (1999) and Aschwanden et al (1999Aschwanden et al ( , 2000aAschwanden et al ( , 2000b.…”

Section: Introductionmentioning

confidence: 99%

The Extreme‐Ultraviolet Structure and Properties of a Newly Emerged Active Region

Gallagher

Phillips

Lee

et al. 2001

ApJ

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The structure and properties of a newly emerged solar active region (NOAA Active Region 7985) are discussed using the Coronal Diagnostic Spectrometer (CDS) and the Extreme-Ultraviolet Imaging Telescope (EIT) on board the Solar and Heliospheric Observatory. CDS obtained high-resolution EUV spectra in the 308È381 and 513È633 wavelength ranges, while EIT recorded full-disk EUV images in A A the He II (304 Fe IX/X (171 Fe XII (195 and Fe XV (284 bandpasses. Electron density mea-A ), A ), A ), A ) surements from Si IX, Si X, Fe XII, Fe XIII, and Fe XIV line ratios indicate that the region consists of a central high-density core with peak densities of the order of 1.2 ] 1010 cm~3, which decrease monotonically to D5.0 ] 108 cm~3 at the active region boundary. The derived electron densities also vary systematically with temperature. Electron pressures as a function of both active region position and temperature were estimated using the derived electron densities and ion formation temperatures, and the constant pressure assumption was found to be an unrealistic simpliÐcation. Indeed, the active region is found to have a high-pressure core (1.3 ] 1016 cm~3 K) that falls to 6.0 ] 1014 cm~3 K just outside the region. CDS line ratios from di †erent ionization stages of iron, speciÐcally Fe XVI (335.4and Fe XIV A ) (334.4 were used to diagnose plasma temperatures within the active region. Using this method, peak A ), temperatures of 2.1 ] 106 K were identiÐed. This is in good agreement with electron temperatures derived using EIT Ðlter ratios and the two-temperature model of Zhang et al. The high-temperature emission is conÐned to the active region core, while emission from cooler (1È1.6) ] 106 K lines originates in a system of loops visible in EIT 171 and 195 images. Finally, the three-dimensional geometry of the A active region is investigated using potential Ðeld extrapolations from a Kitt Peak magnetogram. The combination of EUV and magnetic Ðeld extrapolations extends the "" core-halo ÏÏ picture of active region structure to one in which the core is composed of a number of compact coronal loops that conÐne the hot, dense, high-pressure core plasma while the halo emission emerges from a system of cooler and more extended loops.

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“…In the famous RTV model proposed by Rosner, Tucker and Vaiana (1978), coronal loops were thought to be uniformly heated. but Aschwanden et al (2000) favored the footpoint heating, because such a nonuniform heating model was more consistent with the flat temperature distribution derived from TRACE data. However, it is still an open question.…”

Section: Heating Of Hydrostatic and Hydrodynamic Loopsmentioning

confidence: 61%

Progress in the Heating of Active Region Loops

Feng¹,

Gan²

2004

Proc. IAU

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Abstract. Coronal heating is an important problem in solar physics. With the development of highly qualified instruments, such as TRACE, SOHO and Yohkoh, more and more observations about coronal loops have been obtained. The coronal loops' heating, being an important ingredient of coronal heating, has been paid particular attentions recently. But there are still some key issues about the structure and mechanism of the loops' heating unresolved. In this paper, after a brief review on the latest progress in both observations and modeling of coronal loops, we emphatically discuss the heating of hydrostatic loops and hydrodynamic loops based on the 1D model. The prospect of the subject is presented.

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Evidence for Nonuniform Heating of Coronal Loops Inferred from Multithread Modeling ofTRACEData

Cited by 265 publications

References 38 publications

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

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

The Extreme‐Ultraviolet Structure and Properties of a Newly Emerged Active Region

Progress in the Heating of Active Region Loops

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