Global Energetics of Solar Flares. Ii. Thermal Energies

Aschwanden, Markus J.; Boerner, P.; Ryan, Daniel; Caspi, Amir; McTiernan, J.; Warren, H. P.

doi:10.1088/0004-637x/802/1/53

Cited by 76 publications

(87 citation statements)

References 40 publications

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“…Evidence for multithermal plasmas has been found by EUV and SXR spectroscopy (e.g., Dere & Cook 1979;McTiernan et al 1999;Chifor et al 2007) and by RHESSI HXR observations (Aschwanden 2007;Caspi & Lin 2010;Jain et al 2011). Recent studies using multiband EUV images from SDO/AIA Ryan et al 2014;Aschwanden et al 2015) and EUV spectra by SDO/EVE (Warren et al 2013;Kennedy et al 2013;Caspi et al 2014b) and by Hinode/EIS (Graham et al 2013) have finally provided well-constrained DEM distributions and have shown conclusively that the thermal component in solar flares is indeed multithermal in nature. The DEM distributions derived in these studies tend to be broad, and often a bimodal distribution is found, with a low-temperature peak at 1-2 MK (which is probably due to non-flaring foreground and background coronal material; cf.…”

Section: Evolutionary Effects and Multithermalitymentioning

confidence: 93%

Constraints on energy release in solar flares from RHESSI and GOES X-ray observations

Warmuth

Mann

2016

A&A

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Aims. We constrain energy release and particle acceleration processes in solar flares by means of comprehensively characterizing the physical parameters of both the thermal plasma and the accelerated nonthermal particles using X-ray data. Our aim is to bridge the gap between detailed case studies and large statistical studies. Methods. We obtained time series of spectral fits and images for 24 flares ranging from GOES class C3.4 to X17.2 using RHESSI hard X-ray observations. These data were used to derive basic physical parameters for the thermal plasma (using the isothermal approximation) and the injected nonthermal electrons (assuming the thick-target model). For the thermal component, this was supplemented by GOES soft X-ray data. We derived the ranges and distributions of the various parameters, the scaling with flare importance, and the relation between thermal parameters derived from RHESSI and GOES. Finally, we investigated the relation between thermal and nonthermal parameters. Results. Temperature and emission measure of the thermal plasma are strongly correlated with the peak GOES X-ray flux. Higher emission measures result both from a larger source volume and a higher density, with the latter effect being more important. RHESSI consistently gives higher temperatures and lower emission measures than GOES does, which is a signature of a multithermal plasma. The discrepancy between RHESSI and GOES is particularly pronounced in the early flare phase, when the thermal X-ray sources tend to be large and located higher in the corona. The energy input rate by nonthermal electrons is correlated with temperature and with the increase rate of emission measure and thermal energy. Conclusions. The derived relations between RHESSI-and GOES-derived thermal parameters and the relation between thermal parameters and energy input by nonthermal electrons are consistent with a two-component model of the thermal flare plasma. Both RHESSI and GOES observe a cooler plasma component (≈10−25 MK) that is generated by chromospheric evaporation caused by a nonthermal electron beam. In addition, a hotter component (≥25 MK) is only detected by RHESSI; this component is more consistent with direct in situ heating of coronal plasma. With the exception of the early impulsive phase, RHESSI observes a combination of the evaporated and the directly heated component.

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Section: Evolutionary Effects and Multithermalitymentioning

confidence: 93%

Constraints on energy release in solar flares from RHESSI and GOES X-ray observations

Warmuth

Mann

2016

A&A

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“…We applied standard DEM-analysis (Aschwanden et al 2015) to estimate the radiation losses and the maximum thermal energy using the AIA observations. This analysis covers plasma , as in the work of Aschwanden et al (2015) for the flares.…”

Section: Goes Radmentioning

confidence: 99%

Flare Energy Release in the Lower Solar Atmosphere near the Magnetic Field Polarity Inversion Line

Sharykin

Sadykov

Kosovichev

et al. 2017

ApJ

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“…Such a configuration can be quantified by the differential emission measure (DEM), and recent EUV observations have confirmed that broad DEM distributions are common in solar flares (cf. Fletcher et al 2013;Graham et al 2013;Kennedy et al 2013;Warren et al 2013;Caspi et al 2014b;Ryan et al 2014;Aschwanden et al 2015).…”

Section: Nonisothermality Of the Thermal Plasmamentioning

confidence: 99%

“…Generally, the isothermal assumption will underestimate the thermal and radiative energies, in particular if a significant part of the DEM is outside the instrument temperature response. Recently, Aschwanden et al (2015) have derived the thermal energies for 400 M and X-class flares using DEMs derived from AIA multi-filter observations in the EUV. They found that using the isothermal assumption underestimates the thermal energy by a factor of ≈14 compared to the multithermal case.…”

Section: Nonisothermality Of the Thermal Plasmamentioning

confidence: 99%

“…Recently, the quantitative characterization of multithermality has become possible with differential emission measure distributions (DEMs) derived from a new generation of extreme ultraviolet (EUV) multi-filter imagers (SDO/AIA) as well as spectrographs (SDO/EVE, Hinode/EIS) that provide the required spectral resolution and coverage. Now these DEMs are starting to be used to obtain thermal energies (Aschwanden et al 2015).…”

Section: Introductionmentioning

confidence: 99%

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Constraints on energy release in solar flares from RHESSI and GOES X-ray observations

Warmuth

Mann

2016

A&A

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Aims. We derive constraints on energy release, transport and conversion processes in solar flares based on a detailed characterization of the physical parameters of both the thermal plasma and the accelerated nonthermal electrons based on X-ray observations. In particular, we address the questions of whether the energy required to heat the thermal plasma can be supplied by nonthermal particles, and how the energetics derived from X-rays compare to the total bolometric radiated energy. Methods. Time series of spectral fits and images for 24 flares ranging from GOES class C3.4 to X17.2 were obtained using RHESSI hard X-ray observations. This has been supplemented by GOES soft X-ray fluxes. In our companion Paper I, we have used this data set to obtain the basic physical parameters for the thermal plasma (using the isothermal approximation) and the injected energetic electrons (assuming the thick-target model). Here, we used this data set to derive the flare energetics, including thermal energy, radiative and conductive energy loss, gravitational and flow energy of the plasma, and kinetic energy of the injected electrons. We studied how the thermal energies compare to the energy in nonthermal electrons, and how the various energetics and energy partition depend on flare importance. Results. All flare energetics show a good to excellent correlation with the peak GOES flux. The gravitational energy of the evaporated plasma and the kinetic energy of plasma flows can be neglected in the discussion of flare energetics. The radiative energy losses are comparable to the maximum thermal energy, while the conductive losses are considerably higher than the maximum thermal energy, especially in weaker flares. The total heating requirement of the hot plasma amounts to ≈50% of the total bolometric energy loss, with the conductive losses as a major contribution. The nonthermal energy input by energetic electrons is not sufficient to account for the total heating requirements of the hot plasma or for the bolometric losses, in particular in weak flares. Conclusions. Our results support the standard model of solar flares, with the following modifications. (1) Heating the hot thermal plasma and supplying the bolometric radiated energy requires an additional non-beam heating mechanism. (2) Strong conductive losses are a necessary additional energy transport process that transfers the energy released in the corona to the lower (and denser) atmospheric layers, where the bulk of the released energy is efficiently radiated away at longer wavelengths (EUV, UV, and white light) by cooler material.

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Global Energetics of Solar Flares. Ii. Thermal Energies

Cited by 76 publications

References 40 publications

Constraints on energy release in solar flares from RHESSI and GOES X-ray observations

Constraints on energy release in solar flares from RHESSI and GOES X-ray observations

Flare Energy Release in the Lower Solar Atmosphere near the Magnetic Field Polarity Inversion Line

Constraints on energy release in solar flares from RHESSI and GOES X-ray observations

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