SDO AIA and EVE observations and modelling of solar flare loops

Petkaki, P.; Zanna, G. Del; Mason, H. E.; Bradshaw, S. J.

doi:10.1051/0004-6361/201219812

Cited by 31 publications

(50 citation statements)

References 39 publications

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“…When the Fe xviii emission becomes dominant, we found good agreement between observations and theory (Petkaki et al 2012), suggesting that the AIA 94 Å calibration is correct, given that the atomic data we provided for Fe xviii should be reliable (Witthoeft et al 2006;Del Zanna 2006).…”

Section: Aia 94 åsupporting

confidence: 72%

“…When flare-like emission is present, significant continuum and Fe xxi (formed around 10 MK) emission is present in the 131 Å band, with some contribution also from Fe xx and Fe xxiii (see Petkaki et al 2012;Del Zanna & Woods 2013 shows the total AIA count rates due to the Fe xii 186.8, 192.4, 193.5, and 195.1 Å lines, all observed by EIS. These count rates were obtained by converting the EIS calibrated radiances into AIA DN/s.…”

Section: Aia 131 åmentioning

confidence: 99%

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The multi-thermal emission in solar active regions

Zanna¹

2013

A&A

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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: Aia 94 åsupporting

confidence: 72%

Section: Aia 131 åmentioning

confidence: 99%

The multi-thermal emission in solar active regions

Zanna¹

2013

A&A

Self Cite

155

110

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“…These empirical adjustments do not have any justification when one considers in detail the underlying atomic data. For example, these adjustments modify the high-temperature peaks of the two bands, which are dominated by well-known lines from Fe xviii and Fe xxi (O'Dwyer et al 2010;Petkaki et al 2012), for which the atomic data are accurate.…”

Section: Aia Responsesmentioning

confidence: 99%

CHIANTI – An atomic database for emission lines. Version 8

Zanna

Dere

Young

et al. 2015

A&A

Self Cite

436

407

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We present version 8 of the CHIANTI database. This version includes a large amount of new data and ions, which represent a significant improvement in the soft X-ray, extreme UV (EUV) and UV spectral regions, which several space missions currently cover. New data for neutrals and low charge states are also added. The data are assessed, but to improve the modelling of low-temperature plasma the effective collision strengths for most of the new datasets are not spline-fitted as previously, but are retained as calculated. This required a change of the format of the CHIANTI electron excitation files. The format of the energy files has also been changed. Excitation rates between all the levels are retained for most of the new datasets, so the data can in principle be used to model highdensity plasma. In addition, the method for computing the differential emission measure used in the CHIANTI software has been changed.

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“…The first event was the GOES C1.2 flare on 2011 March 3, UT 19:24-19:44, which was thoroughly studied by Petkaki et al (2012) and who found that the 94 Å emission band was dominated by the Fe xviii line and the 131 Å band by the Fe xxi line, which correspond to the hot contributions. Therefore, to avoid overprocessing we have used the original AIA observations.…”

Section: Datamentioning

confidence: 99%

“…In the study of the dynamics of a small flare, Petkaki et al (2012) perform a similar temporal background subtraction selecting the value of the lowest total emission in the 94 Å and 131 Å channels. Figure 3 maps the background-subtracted 94 Å intensity along the five loops through time.…”

Section: Loop Identification and Definition Of The Inter-moss Regionmentioning

confidence: 99%

HEATING MECHANISMS FOR INTERMITTENT LOOPS IN ACTIVE REGION CORES FROM AIA/SDOEUV OBSERVATIONS

Cadavid

Lawrence

Christian

et al. 2014

ApJ

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We investigate intensity variations and energy deposition in five coronal loops in active region cores. These were selected for their strong variability in the AIA/SDO 94 Å intensity channel. We isolate the hot Fe xviii and Fe xxi components of the 94 Å and 131 Å by modeling and subtracting the "warm" contributions to the emission. HMI/SDO data allow us to focus on "inter-moss" regions in the loops. The detailed evolution of the inter-moss intensity time series reveals loops that are impulsively heated in a mode compatible with a nanoflare storm, with a spike in the hot 131 Å signals leading and the other five EUV emission channels following in progressive cooling order. A sharp increase in electron temperature tends to follow closely after the hot 131 Å signal confirming the impulsive nature of the process. A cooler process of growing emission measure follows more slowly. The Fourier power spectra of the hot 131 Å signals, when averaged over the five loops, present three scaling regimes with break frequencies near 0.1 min −1 and 0.7 min −1 . The low frequency regime corresponds to 1/f noise; the intermediate indicates a persistent scaling process and the high frequencies show white noise. Very similar results are found for the energy dissipation in a 2D "hybrid" shell model of loop magneto-turbulence, based on reduced magnetohydrodynamics, that is compatible with nanoflare statistics. We suggest that such turbulent dissipation is the energy source for our loops.

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SDO AIA and EVE observations and modelling of solar flare loops

Cited by 31 publications

References 39 publications

The multi-thermal emission in solar active regions

The multi-thermal emission in solar active regions

CHIANTI – An atomic database for emission lines. Version 8

HEATING MECHANISMS FOR INTERMITTENT LOOPS IN ACTIVE REGION CORES FROM AIA/SDOEUV OBSERVATIONS

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