Hydrodynamic Modeling of Active Region Loops

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

doi:10.1086/344921

Cited by 124 publications

(123 citation statements)

References 18 publications

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“…In this scenario, each of the many hundreds to thousands of strands in the loop is heated impulsively and the heating recurrence time on a single strand is longer than a cooling time. Such loops are then expected to be seen sequentially in cooler channels with time, a pattern confirmed in X-ray and EUV observations (Warren et al 2002;Winebarger et al 2003;Winebarger & Warren 2005;Ugarte-Urra et al 2006, 2009. On the other hand, in the so-called hot cores of ARs, some believe the heating to be predominantly steady, meaning that the heating recurrence time on a strand is much less than the cooling time, and that the emission is exclusively hot.…”

Section: Introductionmentioning

confidence: 59%

“…The idea that loops are heated by nanoflares has been popular for some time (Klimchuk 2006, and references cited therein), and it is now largely agreed upon that warm loops are explained by nanoflare storms with durations of several hundred to several thousand seconds (e.g., Warren et al 2002Warren et al , 2003Winebarger et al 2003;Winebarger & Warren 2005;Klimchuk 2009), although see Mok et al (2008) for an alternative explanation. In this scenario, each of the many hundreds to thousands of strands in the loop is heated impulsively and the heating recurrence time on a single strand is longer than a cooling time.…”

Section: Introductionmentioning

confidence: 99%

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PATTERNS OF NANOFLARE STORM HEATING EXHIBITED BY AN ACTIVE REGION OBSERVED WITHSOLAR DYNAMICS OBSERVATORY/ATMOSPHERIC IMAGING ASSEMBLY

Viall

Klimchuk

2011

ApJ

110

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It is largely agreed that many coronal loops-those observed at a temperature of about 1 MK-are bundles of unresolved strands that are heated by storms of impulsive nanoflares. The nature of coronal heating in hotter loops and in the very important but largely ignored diffuse component of active regions is much less clear. Are these regions also heated impulsively, or is the heating quasi-steady? The spectacular new data from the Atmospheric Imaging Assembly (AIA) telescopes on the Solar Dynamics Observatory offer an excellent opportunity to address this question. We analyze the light curves of coronal loops and the diffuse corona in six different AIA channels and compare them with the predicted light curves from theoretical models. Light curves in the different AIA channels reach their peak intensities with predictable orderings as a function the nanoflare storm properties. We show that while some sets of light curves exhibit clear evidence of cooling after nanoflare storms, other cases are less straightforward to interpret. Complications arise because of line-of-sight integration through many different structures, the broadband nature of the AIA channels, and because physical properties can change substantially depending on the magnitude of the energy release. Nevertheless, the light curves exhibit predictable and understandable patterns consistent with impulsive nanoflare heating.

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Section: Introductionmentioning

confidence: 59%

Section: Introductionmentioning

confidence: 99%

PATTERNS OF NANOFLARE STORM HEATING EXHIBITED BY AN ACTIVE REGION OBSERVED WITHSOLAR DYNAMICS OBSERVATORY/ATMOSPHERIC IMAGING ASSEMBLY

Viall

Klimchuk

2011

ApJ

110

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“…The loops presented here seem to have similar characteristics to the former. Recently, Warren et al (2002) proposed an impulsive heating model, where loops are made out of finer magnetic strands that get impulsively and sequentially heated. The model predicts that the strands, before cooling and being observed in the EUV TRACE images, could be heated to large temperatures that fall in the range where SXT is sensitive.…”

Section: Discussionmentioning

confidence: 99%

“…Even though these loops persist much longer than their characteristic cooling times, the filter ratio along the loops and large apex emission measures cannot be reproduced by steady heating models (Lenz et al 1999;Aschwanden et al 2001;Winebarger et al 2003). Warren et al (2002) found that an impulsive heating mechanism could produce the large densities needed to account for the emission, while a bundle of strands sequentially heated would reproduce the observed lifetimes. In such a model, the cooling strands, understood as the finer structure of the unresolved loops, would be observed at different times by filters sensitive to different temperature regimes.…”

Section: Introductionmentioning

confidence: 97%

An Investigation into the Variability of Heating in a Solar Active Region

Ugarte-Urra

Winebarger

Warren

2006

ApJ

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Previous studies have indicated that both steady and impulsive heating mechanisms play a role in active region heating. In this paper, we present a study of 20 hours of soft X-ray and EUV observations of solar active region NOAA AR 8731. We examine the evolution of six representative loop structures that brighten and fade first from X-ray images and subsequently from the EUV images. We determine their lifetime and the delay between their appearance in the different filters. We find that the lifetime in the EUV filters is much longer than expected for a single cooling loop. We also notice that the delay in the loops' appearance in the X-ray and EUV filters is proportional to the loop length. We model one of the loops using a hydrodynamic model with both impulsive and quasisteady heating functions and find that neither of these simple heating functions can well reproduce the observed loop characteristics in both the X-ray and EUV images. Hence, although this active region is dominated by variable emission and the characteristics of the observed loops are qualitatively consistent with a cooling loop, the timescale of the heating in this active region remains unknown.

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“…These clusters of events can be considered to be the same as 'nanoflare storms' [88] that typically last several hundred to several thousand seconds. These were introduced (even though not coining this name) to match the light curves of warm loops in one-dimensional models [89]. The three-dimensional MHD models show that not only nanoflares but also the storms are a natural consequence of the fieldline braiding and flux-tube tectonics governing the energy deposition [85].…”

Section: (E) Nanoflares Nanoflare Storms and Braiding Of Fieldlinesmentioning

confidence: 99%

What can large-scale magnetohydrodynamic numerical experiments tell us about coronal heating?

Peter

2015

Phil. Trans. R. Soc. A.

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The upper atmosphere of the Sun is governed by the complex structure of the magnetic field. This controls the heating of the coronal plasma to over a million kelvin. Numerical experiments in the form of threedimensional magnetohydrodynamic simulations are used to investigate the intimate interaction between magnetic field and plasma. These models allow one to synthesize the coronal emission just as it would be observed by real solar instrumentation. Largescale models encompassing a whole active region form evolving coronal loops with properties similar to those seen in extreme ultraviolet light from the Sun, and reproduce a number of average observed quantities. This suggests that the spatial and temporal distributions of the heating as well as the energy distribution of individual heat deposition events in the model are a good representation of the real Sun. This provides evidence that the braiding of fieldlines through magneto-convective motions in the photosphere is a good concept to heat the upper atmosphere of the Sun.

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Hydrodynamic Modeling of Active Region Loops

Cited by 124 publications

References 18 publications

PATTERNS OF NANOFLARE STORM HEATING EXHIBITED BY AN ACTIVE REGION OBSERVED WITHSOLAR DYNAMICS OBSERVATORY/ATMOSPHERIC IMAGING ASSEMBLY

PATTERNS OF NANOFLARE STORM HEATING EXHIBITED BY AN ACTIVE REGION OBSERVED WITHSOLAR DYNAMICS OBSERVATORY/ATMOSPHERIC IMAGING ASSEMBLY

An Investigation into the Variability of Heating in a Solar Active Region

What can large-scale magnetohydrodynamic numerical experiments tell us about coronal heating?

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