Enthalpy-Based Thermal Evolution of Loops. Ii. Improvements to the Model

Cargill, P. J.; Bradshaw, S. J.; Klimchuk, J. A.

doi:10.1088/0004-637x/752/2/161

Cited by 113 publications

(171 citation statements)

References 27 publications

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“…We also use another free parameter to characterize the loss term through the transition region. Instead of computing this loss term using an equilibrium solution (Cargill et al 2012a), we scale this term as being proportional to the mean coronal pressure P á ñ by a scaling constant η. Such proportionality is observed in the decay phase of solar and stellar flares as well as predicted in coronal heating models (Hawley & Fisher 1992;Qiu et al 2013, and references therein).…”

Section: D Modeling Of 12500 Loopsmentioning

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: D Modeling Of 12500 Loopsmentioning

confidence: 99%

Long Duration Flare Emission: Impulsive Heating or Gradual Heating?

Qiu

Longcope

2016

ApJ

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“…However, it is unclear how successfully this formalism translates into dynamic evolution. The increase in coronal density after heating arises precisely because the transition region is not in equilibrium: the downward heat flux exceeding the radiative losses, leading to an upward enthalpy flux (see Klimchuk et al 2008;Cargill et al 2012). In the decay of impulsive events, the coronal properties are governed by a downward enthalpy flux responsible for the transition region radiation: conduction plays a minimal role (Bradshaw 2008;Bradshaw & Cargill 2010a, 2010b.…”

Section: Implications For Multi-dimensional Mhd Modelsmentioning

confidence: 99%

“…Hotter loops require smaller grid cells and longer loops can be modeled with wider cells. Such resolutions are straightforward in static loop models, either by brute force or especially using thermally structured grids (e.g., Appendix A of Cargill et al 2012).…”

Section: Introductionmentioning

confidence: 99%

The Influence of Numerical Resolution on Coronal Density in Hydrodynamic Models of Impulsive Heating

Bradshaw

Cargill

2013

ApJ

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The effect of the numerical spatial resolution in models of the solar corona and corona/chromosphere interface is examined for impulsive heating over a range of magnitudes using one-dimensional hydrodynamic simulations. It is demonstrated that the principal effect of inadequate resolution is on the coronal density. An underresolved loop typically has a peak density of at least a factor of two lower than a resolved loop subject to the same heating, with larger discrepancies in the decay phase. The temperature for underresolved loops is also lower indicating that lack of resolution does not "bottle up" the heat flux in the corona. Energy is conserved in the models to under 1% in all cases, indicating that this is not responsible for the low density. Instead, we argue that in underresolved loops the heat flux "jumps across" the transition region to the dense chromosphere from which it is radiated rather than heating and ablating transition region plasma. This emphasizes the point that the interaction between corona and chromosphere occurs only through the medium of the transition region. Implications for three-dimensional magnetohydrodynamic coronal models are discussed.

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“…The net loss includes the optically-thin radiative loss in the corona and an amount of loss through the transition region, part of which will be radiated by the chromosphere. The loss through the transition region is either directly scaled to the coronal radiative loss with a free scaling parameter (Klimchuk et al 2008), or estimated by taking into account the atmosphere stratification (Cargill et al 2012a). In this study, we have computed loop evolution with both versions of the code, and found that the difference is only about 10% in both the temperature and density values.…”

Section: Modeling Of the Two Sets Of Flare Loopsmentioning

confidence: 97%

“…We use these heating rates to compute plasma evolution in flare loops using the zerodimensional (0D) model called "enthalpy-based thermal evolution of loops" (EBTEL; Klimchuk et al 2008;Cargill et al 2012a) in this study. The EBTEL model computes evolution of the average temperature and density in a coronal loop given an impulsive energy input, which has been validated by advanced one-dimensional (1D) hydrodynamic simulations.…”

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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Enthalpy-Based Thermal Evolution of Loops. Ii. Improvements to the Model

Cited by 113 publications

References 27 publications

Long Duration Flare Emission: Impulsive Heating or Gradual Heating?

Long Duration Flare Emission: Impulsive Heating or Gradual Heating?

The Influence of Numerical Resolution on Coronal Density in Hydrodynamic Models of Impulsive Heating

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

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