Mass motions in a heated flare filament

Craig, I. J. D.; McClymont, A. N.

doi:10.1007/bf00206198

Cited by 36 publications

(17 citation statements)

References 16 publications

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“…The plasma along these loops is heated to flare temperatures both by the reconnection itself and by the subsequent contraction of the loop under magnetic tension (Longcope et al 2009). The energy from this flare plasma is then transported down the legs of the loop by nonthermal particles (Brown 1973), thermal conduction (Craig & McClymont 1976;Forbes et al 1989), wave propagation (Russell & Fletcher 2013), or some other means, until it reaches the cool, dense chromospheric plasma located at the loop footpoints. Energy is rapidly deposited in the chromosphere and transition region (TR), resulting in plasma flows both up and down the loop.…”

Section: Introductionmentioning

confidence: 99%

Spectroscopic Observations of an Evolving Flare Ribbon Substructure Suggesting Origin in Current Sheet Waves

Brannon

Longcope

Qiu

2015

ApJ

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We present imaging and spectroscopic observations from the Interface Region Imaging Spectrograph of the evolution of the flare ribbon in the SOL2014-04-18T13:03 M-class flare event, at high spatial resolution and time cadence. These observations reveal small-scale substructure within the ribbon, which manifests as coherent quasiperiodic oscillations in both position and Doppler velocities. We consider various alternative explanations for these oscillations, including modulation of chromospheric evaporation flows. Among these, we find the best support for some form of wave localized to the coronal current sheet, such as a tearing mode or Kelvin-Helmholtz instability.

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Section: Introductionmentioning

confidence: 99%

Spectroscopic Observations of an Evolving Flare Ribbon Substructure Suggesting Origin in Current Sheet Waves

Brannon

Longcope

Qiu

2015

ApJ

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“…Therefore, much effort has been devoted to numerical solutions of both the hydrodynamic response of the flare loop [11][12][13][14][15][16][17][18][19][20] as well as calculations of the radiative output of semi-empirical flare models [21,22]. It is clear, however, that the most complete approach is the self-consistent solution of both the equations of hydrodynamics and radiation transport in the flaring loop.…”

Section: A the Equationsmentioning

confidence: 99%

Radiation Hydrodynamics in Solar Flares

Fisher

1986

International Astronomical Union Colloquium

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Solar flares are currently understood as the explosive release of energy stored in the form of stressed magnetic fields. In many cases, the released energy seems to take the form of large numbers of electrons accelerated to high energies (the nonthermal electron "thick target" model), or alternatively plasma heated to very high temperatures behind a rapidly moving conduction front (the "thermal" model). The transport of this energy into the remaining portion of the atmosphere results in violent mass motion and strong emission across the electromagnetic spectrum. Radiation processes play a crucial role in determining the ensuing plasma motion.One important phenomenon observed during flares is the appearance in coronal magnetic loops of large amounts of upflowing, soft X-ray emitting plasma at temperatures of 1 − 2 × 10 7 [K]. It is believed that this is due to chromospheric evaporation, the process of heating cool (T ∼ 10 4 [K]) chromospheric material beyond its ability to radiate. Detailed calculations of thick target heating show that if nonthermal electrons heat the chromosphere directly, then the evaporation process can result in explosive upward motion of X-ray emitting plasma if the heating rate exceeds a threshold value. In such a case, upflow velocities approach an upper limit of roughly 2.35c s as the heating rate is increased beyond the threshold, where c s is the sound speed in the evaporated plasma. This is known as explosive evaporation. If the flare heating rate is less than the threshold, evaporation takes place indirectly through thermal conduction of heat deposited in the corona by the energetic electrons. Upflows in this case are roughly 10 to 20% of the upper limit. Evaporation by thermal model heating always takes place through thermal conduction, and the computed upflow speeds seem to be about 10% to 20% of the upper limit, independent of the energy flux.The pressure increase in the evaporated plasma for either the thick target or thermal model leads to a number of interesting phenomena in the flare chromosphere. The sudden pressure increase initiates a downward moving "chromospheric condensation", an overdense region which gradually decelerates as it -2 -accretes material and propagates into the gravitationally stratified chromosphere. Solutions to an equation of motion for this condensation shows that its motion decays after about one minute of propagation into the chromosphere. When the front of this downflowing region is supersonic relative to the atmosphere ahead of it, a radiating shock will form. If the downflow is rapid enough, the shock strength should be sufficient to excite UV radiation normally associated with the transition region, and furthermore, the radiating shock will be brighter than the transition region. These results lead to a number of observationally testable relationships between the optical and ultraviolet spectra from the condensation and radiating shock.

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“…Other loop parameters are as defined in Table I. Our aim is to relate the evolution of the differential emission measure 2n 2 dT-1 ~(T)= I~zzl cm-5 (6.1) which governs the X-ray and EUV spectrum of the plasma (Craig and Brown, 1976) to the dynamic processes within the loop. Figures 5 and 6 indicate the loop dynamics while Figures 7 and 8 illustrate the temperature-emission measure structure of the plasma.…”

Section: Loop Dynamics: Observational Consequencesmentioning

confidence: 99%

“…Kostyuk and Pikelner, 1975;Craig andMcClymont, 1976, 1981). This trend has been encouraged by a wealth of observational data, typically in the X-ray EUV and optical wavebands, which indicate that significant mass flows can occur in all temperature regimes of the flare plasma (-104-107 K).…”

Section: Introductionmentioning

confidence: 99%

“…That is, a static model for the loop structure is assumed, and the dynamic response of the loop to non-stationary heating is investigated: The problem is to determine evolutionary profiles for the temperature, density and fluid velocity of the flare. However, it has recently been argued that certain static loop configurations may be radiatively unstable (Antiochos, 1979;Hood and Priest, 1079;Craig and McClymont, 1981). This is serious in the context of dynamic flare modelling since it implies that the dynamic solution, even assuming its existence and uniqueness (see below), may depend discontinuously on the initial atmosphere; that is, the solution may be governed by the nature of infinitesimal perturbations in the initial state (see Antiochos, 1979).…”

Section: Introductionmentioning

confidence: 99%

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The stability and uniqueness of coronal loops

1982

Self Cite

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A hydrodynamic model of high resolution is used to examine the stability of coronal loops to finite amplitude perturbations. The loop is heated by means of a low-amplitude energy input and its subsequent dynamic relaxation is followed.Firstly, the initial atmosphere is generated by solving the time independent form of the hydrodynamic equations. It is shown that the loop structure depends critically on the balance between the radiative losses and the quiescent heating at the base of the transition zone, i.e. on the concavity of the temperature profile in this region. This result already anticipates the need for high spatial resolution across the model transition zone.The dynamic evolution of the loop is then investigated for two classes of lower boundary conditions. In one case the chromospheric temperature is fixed throughout the simulation; in the other the low chromosphere is represented by a rigid insulating barrier. In both cases the loop is found to be stable: The loop is also unique to the extent that it relaxes to a state which is physically indistinguishable from its initial configuration. It is pointed out however, that a loop whose chromosphere is only marginally stable can evolve dynamically away from the initial static configuration.Finally, the observational consequences of the analysis are discussed. The differential emission measure profile is found to change its form as the loop cools, firstly, through an evaporative phase in which the coronal density increases; secondly, through a quasi-steady relaxation in which the enhanced coronal density gradually drains away to the chromosphere. This behaviour represents a possible observational test of the model.

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Mass motions in a heated flare filament

Cited by 36 publications

References 16 publications

Spectroscopic Observations of an Evolving Flare Ribbon Substructure Suggesting Origin in Current Sheet Waves

Spectroscopic Observations of an Evolving Flare Ribbon Substructure Suggesting Origin in Current Sheet Waves

Radiation Hydrodynamics in Solar Flares

The stability and uniqueness of coronal loops

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