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

Ugarte-Urra, Ignacio; Winebarger, Amy R.; Warren, H. P.

doi:10.1086/503196

Cited by 63 publications

(70 citation statements)

References 42 publications

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“…do not appear to cool down or heat up significantly over timescales of hours Cirtain et al 2007). Our results are in contrast to those obtained by Warren et al (2003); Ugarte-Urra et al (2006Viall & Klimchuk (2011), although they do not necessarily imply steady heating for the single structures. Indeed the higher SDO AIA resolution shows clear variations on timescales of minutes.…”

Section: )contrasting

confidence: 99%

The multi-thermal emission in solar active regions

Zanna¹

2013

A&A

155

110

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We present simultaneous SDO AIA and Hinode EIS observations of the hot cores of active regions (ARs) and assess the dominant contributions to the AIA EUV bands. This is an extension of our previous work. We find good agreement between SDO AIA, EVE and EIS observations, using our new EIS calibration and the latest EVE v.3 data. We find that all the AIA bands are multi-thermal, with the exception of the 171 and 335 Å, and provide ways to roughly estimate the main contributions directly from the AIA data. We present and discuss new atomic data for the AIA bands, showing that they are now sufficiently complete to obtain temperature information in the cores of ARs, with the exception of the 211 Å band. We found that the newly identified Fe xiv 93.61 Å line is the dominant contribution to the 94 Å band, whenever Fe xviii is not present. Three methods to estimate the Fe xviii emission in this band are presented, two using EIS and one directly from the AIA data. Fe xviii emission is often present in the cores of ARs, but we found cases where it is formed at 3 MK and not 7 MK, the temperature of peak ion abundance in equilibrium. The best EIS lines for elemental abundance determination and differential emission measure (DEM) analysis are discussed. A new set of abundances for many elements are obtained from EIS observations of hot 3 MK loops. The abundances of the elements with low first ionisation potential (FIP), relative to those of the high-FIP elements, are found to be enhanced by about a factor of three, compared to the photospheric values. A measurement of the path length implies that the absolute abundances of the low-FIP elements are higher than the photospheric values by at least a factor of three. We present a new DEM method customised for the AIA bands, to study the thermal structure of ARs at 1 resolution. This was tested on a few ARs, including one observed during the Hi-C rocket flight. We found excellent agreement between predicted and observed AIA count rates and EIS radiances. Overall we found few differences between the AIA and Hi-C 193 Å images of coronal structures, despite the higher Hi-C resolution (0.25 ). The Hi-C images and the AIA DEM modelling suggest that some of the cooler loops (below 1 MK) are already resolved by AIA, while the hotter (1.5-2.5 MK) "background" emission is in most places still unresolved even at the Hi-C resolution. This unresolved emission is significantly lower than previously observed with TRACE, the SOHO CDS, and Hinode EIS spectrometers. Its enhancement appears to be mostly due to increased iron abundance. We find an ubiquitous presence of emission at different temperatures that is not co-spatial, and suggest that future high-resolution imaging is carried out with isothermal bands.

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Section: )contrasting

confidence: 99%

The multi-thermal emission in solar active regions

Zanna¹

2013

A&A

155

110

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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: 62%

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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“…There are also indicators that hydrodynamic evolution along coronal loops can be quite common, especially for active regions. These include observations of coronal rain and catastrophic cooling cycles (Schrijver 2001;Antolin & Rouppe van der Voort 2012;Antolin et al 2015), as well as pervasive cooling signatures observed in extreme ultraviolet (Viall & Klimchuk 2011Auchère et al 2014;Froment et al 2015) and soft X-Ray imaging (Ugarte- Urra et al 2006). A successful heating model should be plausibly consistent with such observations.…”

Section: Introductionmentioning

confidence: 91%

Closed-Field Coronal Heating Driven by Wave Turbulence

Downs

Lionello

Mikić

et al. 2016

ApJ

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To simulate the energy balance of coronal plasmas on macroscopic scales, we often require the specification of the coronal heating mechanism in some functional form. To go beyond empirical formulations and to build a more physically motivated heating function, we investigate the wave-turbulence-driven (WTD) phenomenology for the heating of closed coronal loops. Our implementation is designed to capture the large-scale propagation, reflection, and dissipation of wave turbulence along a loop. The parameter space of this model is explored by solving the coupled WTD and hydrodynamic evolution in 1D for an idealized loop. The relevance to a range of solar conditions is also established by computing solutions for over one hundred loops extracted from a realistic 3D coronal field. Due to the implicit dependence of the WTD heating model on loop geometry and plasma properties along the loop and at the footpoints, we find that this model can significantly reduce the number of free parameters when compared to traditional empirical heating models, and still robustly describe a broad range of quiet-sun and active region conditions. The importance of the self-reflection term in producing relatively short heating scale heights and thermal nonequilibrium cycles is also discussed.

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

Cited by 63 publications

References 42 publications

The multi-thermal emission in solar active regions

The multi-thermal emission in solar active regions

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

Closed-Field Coronal Heating Driven by Wave Turbulence

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