PATTERNS OF NANOFLARE STORM HEATING EXHIBITED BY AN ACTIVE REGION OBSERVED WITH<i>SOLAR DYNAMICS OBSERVATORY</i>/ATMOSPHERIC IMAGING ASSEMBLY

Viall, N. M.; Klimchuk, J. A.

doi:10.1088/0004-637x/738/1/24

Cited by 112 publications

(120 citation statements)

References 28 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

159

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

159

110

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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].…”

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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“…SOC seeks to explain power-law distributions of flare parameters via cooperative interactions of a large number of nonlinearly coupled degrees of freedom representing unstable coronal loops and/or loop strands (Crosby et al 1993;Crosby 2011;Charbonneau et al 2001;Aschwanden et al 2000b;Aschwanden & Parnell 2002;Morales & Charbonneau 2008;Uritsky et al 2007). It has been suggested that the nonpotential magnetic field configurations existing in the corona release their free energy through a chain interaction of multiple spatially localized instabilities such as those associated with nanoflare heating (Parker 1988;Klimchuk 2006;Viall & Klimchuk 2011). The perturbation proceeds explosively by involving a growing number of unstable plasma regions, similarly to the interaction of rolling grains of sand leading to a sand pile avalanche (Bak et al 1987(Bak et al , 1988.…”

Section: Routes To Multiscale Dissipationmentioning

confidence: 99%

Stochastic Coupling of Solar Photosphere and Corona

Uritsky¹,

Davila²,

Ofman³

et al. 2013

ApJ

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The observed solar activity is believed to be driven by the dissipation of nonpotential magnetic energy injected into the corona by dynamic processes in the photosphere. The enormous range of scales involved in the interaction makes it difficult to track down the photospheric origin of each coronal dissipation event, especially in the presence of complex magnetic topologies. In this paper, we propose an ensemble-based approach for testing the photosphere-corona coupling in a quiet solar region as represented by intermittent activity in Solar and Heliospheric Observatory Michelson Doppler Imager and Solar TErrestrial RElations Observatory Extreme Ultraviolet Imager image sets. For properly adjusted detection thresholds corresponding to the same degree of intermittency in the photosphere and corona, the dynamics of the two solar regions is described by the same occurrence probability distributions of energy release events but significantly different geometric properties. We derive a set of scaling relations reconciling the two groups of results and enabling statistical description of coronal dynamics based on photospheric observations. Our analysis suggests that multiscale intermittent dissipation in the corona at spatial scales >3 Mm is controlled by turbulent photospheric convection. Complex topology of the photospheric network makes this coupling essentially nonlocal and non-deterministic. Our results are in an agreement with the Parker's coupling scenario in which random photospheric shuffling generates marginally stable magnetic discontinuities at the coronal level, but they are also consistent with an impulsive wave heating involving multiscale Alfvénic wave packets and/or magnetohydrodynamic turbulent cascade. A back-reaction on the photosphere due to coronal magnetic reconfiguration can be a contributing factor.

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

Cited by 112 publications

References 28 publications

The multi-thermal emission in solar active regions

The multi-thermal emission in solar active regions

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

Stochastic Coupling of Solar Photosphere and Corona

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