Evolution of the Loop‐Top Source of Solar Flares: Heating and Cooling Processes

Jiang, Yuming; Liu, Siming; Liu, Wei; Petrosian, V.

doi:10.1086/498863

Cited by 78 publications

(102 citation statements)

References 36 publications

(60 reference statements)

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“…This is not necessarily true (e.g., Shen et al 2013). It has also been discussed that turbulence in flare loops may suppress thermal conduction (Jiang et al 2006;Wang et al 2015, and references therein). The impact of these effects on flare modeling can be examined in the future study.…”

Section: Limitation Of the Modelmentioning

confidence: 99%

Long Duration Flare Emission: Impulsive Heating or Gradual Heating?

Qiu

Longcope

2016

ApJ

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Flare emissions in X-ray and EUV wavelengths have previously been modeled as the plasma response to impulsive heating from magnetic reconnection. Some flares exhibit gradually evolving X-ray and EUV light curves, which are believed to result from superposition of an extended sequence of impulsive heating events occurring in different adjacent loops or even unresolved threads within each loop. In this paper, we apply this approach to a long duration two-ribbon flare SOL2011-09-13T22 observed by the Atmosphere Imaging Assembly (AIA). We find that to reconcile with observed signatures of flare emission in multiple EUV wavelengths, each thread should be heated in two phases, an intense impulsive heating followed by a gradual, low-rate heating tail that is attenuated over 20-30 minutes. Each AIA resolved single loop may be composed of several such threads. The two-phase heating scenario is supported by modeling with both a zero-dimensional and a 1D hydrodynamic code. We discuss viable physical mechanisms for the two-phase heating in a post-reconnection thread.

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Section: Limitation Of the Modelmentioning

confidence: 99%

Long Duration Flare Emission: Impulsive Heating or Gradual Heating?

Qiu

Longcope

2016

ApJ

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“…The power-law spectral index undergoes progressive hardening over the duration of the first three intervals shown in Fig. 6, before showing an apparent abrupt softening between the third and fourth intervals (Jiang et al 2006, Fig. 11).…”

Section: Comparison With Observationsmentioning

confidence: 94%

“…Thus, these observations also show qualitative similarity to our model. Jiang et al (2006) also discuss 5 other coronal sources in detail. All show the emergence of a thermal component from an initial power-law.…”

Section: Comparison With Observationsmentioning

confidence: 99%

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Thermalisation and hard X-ray bremsstrahlung efficiency of self-interacting solar flare fast electrons

Galloway

Helander²,

MacKinnon

et al. 2010

A&A

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Context. Most theoretical descriptions of the production of solar flare bremsstrahlung radiation assume the collision of dilute accelerated particles with a cold, dense target plasma, neglecting interactions of the fast particles with each other. This is inadequate for situations where collisions with this background plasma are not completely dominant, as may be the case in, for example, low-density coronal sources. Aims. We aim to formulate a model of a self-interacting, entirely fast electron population in the absence of a dense background plasma, to investigate its implications for observed bremsstrahlung spectra and the flare energy budget. Methods. We derive approximate expressions for the time-dependent distribution function of the fast electrons using a Fokker-Planck approach. We use these expressions to generate synthetic bremsstrahlung X-ray spectra as would be seen from a corresponding coronal source. Results. We find that our model qualitatively reproduces the observed behaviour of some flares. As the flare progresses, the model's initial power-law spectrum is joined by a lower energy, thermal component. The power-law component diminishes, and the growing thermal component proceeds to dominate the total emission over timescales consistent with flare observations. The power-law exhibits progressive spectral hardening, as is seen in some flare coronal sources. We also find that our model requires a factor of 7−10 fewer accelerated electrons than the cold, thick target model to generate an equivalent hard X-ray flux. Conclusions. This model forms the basis of a treatment of self-interactions among flare fast electrons, a process which affords a more efficient means to produce bremsstrahlung photons and so may reduce the efficiency requirements placed on the particle acceleration mechanism. It also provides a useful description of the thermalisation of fast electrons in coronal sources.

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“…In addition, Cargill & Priest (1983) proposed that the post-flare loop could be heated by magnetohydrodynamic shocks for a long time. Jiang et al (2006) reported that continuous energy input is necessary to balance the rapid radiative cooling for a few flares. Continuous heating is also supported by spectroscopic velocity measurements.…”

Section: Introductionmentioning

confidence: 99%

Heating and Dynamics of Two Flare Loop Systems Observed by Aia and Eis

Qiu

Ding

2014

ApJ

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We investigate heating and evolution of flare loops in a C4.7 two-ribbon flare on 2011 February 13. From SDO/AIA imaging observations, we can identify two sets of loops. Hinode/EIS spectroscopic observations reveal blueshifts at the feet of both sets of loops. The evolution and dynamics of the two sets are quite different. The first set of loops exhibits blueshifts for about 25 minutes followed by redshifts, while the second set shows stronger blueshifts, which are maintained for about one hour. The UV 1600 observation by AIA also shows that the feet of the second set of loops brighten twice. These suggest that continuous heating may be present in the second set of loops. We use spatially resolved UV light curves to infer heating rates in the few tens of individual loops comprising the two loop systems. With these heating rates, we then compute plasma evolution in these loops with the "enthalpy-based thermal evolution of loops" (EBTEL) model. The results show that, for the first set of loops, the synthetic EUV light curves from the model compare favorably with the observed light curves in six AIA channels and eight EIS spectral lines, and the computed mean enthalpy flow velocities also agree with the Doppler shift measurements by EIS. For the second set of loops modeled with twice-heating, there are some discrepancies between modeled and observed EUV light curves in low-temperature bands, and the model does not fully produce the prolonged blueshift signatures as observed. We discuss possible causes for the discrepancies.

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Evolution of the Loop‐Top Source of Solar Flares: Heating and Cooling Processes

Cited by 78 publications

References 36 publications

Long Duration Flare Emission: Impulsive Heating or Gradual Heating?

Long Duration Flare Emission: Impulsive Heating or Gradual Heating?

Thermalisation and hard X-ray bremsstrahlung efficiency of self-interacting solar flare fast electrons

Heating and Dynamics of Two Flare Loop Systems Observed by Aia and Eis

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