Semiempirical models of chromospheric flare regions

Machado, M. E.; Avrett, E. H.; Vernazza, J. E.; Noyes, R. W.

doi:10.1086/158467

Cited by 260 publications

(242 citation statements)

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“…After modeling, we compare our synthetic spectra to the observed IRIS spectra. As the flare was of class X1, we chose the classical semi-empirical flare model F2 of Machado et al (1980). From an extended grid of synthetic line profiles as shown in Avrett, Machado, and Kurucz (1986) we noticed that the Mg ii k line profile corresponding to model F2 is non-reversed, a feature we observe at several positions.…”

Section: Synthetic Spectramentioning

confidence: 99%

“…They have been modeled under the QS conditions (Milkey and Mihalas, 1974;Bocchialini and Gouttebroze, 1996;Uitenbroek, 1997;Leenaarts et al, 2013;Avrett, Landi, and McKillop, 2013), but concerning the flare atmospheres, the only study is that of Avrett, Machado, and Kurucz (1986) who used the well-known semi-empirical flare models of Machado et al (1980) and synthesized the Mg ii k line intensities emergent from F1, F2 and F3 model atmospheres. Lemaire, Choucq-Bruston, and Vial (1984) used the models F1 and F2 and computed their own synthetic intensities to compare with Mg ii OSO-8 observations.…”

Section: Introductionmentioning

confidence: 99%

“…We defined several 'metrics' quantities and show how they evolve in time. We also perform non-LTE radiative-transfer modeling using the semi-empirical model F2 (Machado et al, 1980) as a representative atmospheric snapshot of the temperature and density structure and compare our synthetic Mg ii line intensities with IRIS observations. We use the theoretical energy balance models of Ricchiazzi and Canfield (1983) to study how various electron-beam parameters affect the profiles of the Mg ii lines.…”

Section: Introductionmentioning

confidence: 99%

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Mg ii Lines Observed During the X-class Flare on 29 March 2014 by the Interface Region Imaging Spectrograph

Liu¹,

Heinzel²,

Kleint³

et al. 2016

Solar and Stellar Flares

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Mg ii lines represent one of the strongest emissions from the chromospheric plasma during solar flares. In this article, we studied the Mg ii lines observed during the X1 flare on March 29 2014 (SOL2014-03-29T17:48) by the Interface Region Imaging Spectrograph (IRIS). IRIS detected large intensity enhancements of the Mg ii h and k lines, subordinate triplet lines, and several other metallic lines at the flare footpoints during this flare. We have used the advantage of the slit-scanning mode (rastering) of IRIS and performed, for the first time, a detailed analysis of spatial and temporal variations of the spectra. Moreover, we were also able to identify positions of strongest hard X-ray (HXR) emissions using the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) observations and to correlate them with the spatial and temporal evolution of IRIS Mg ii spectra. The light curves of the Mg ii lines increase and peak contemporarily with the HXR emissions but decay more gradually. There are large red asymmetries in the Mg ii h and k lines after the flare peak. We see two spatially well separated groups of Mg ii line profiles, non-reversed and reversed. In some cases, the Mg ii footpoints with reversed profiles are correlated with HXR sources. We show the spatial and temporal behavior of several other line parameters (line metrics) and briefly discuss them. Finally, we have synthesized the Mg ii k line using our non-LTE code with the Multilevel Accelerated Lambda Iteration (MALI) technique. Two kinds of models are considered, the flare model F2 of Machado et al. (1980, Astrophys. J., 242, 336 ) and the models of Ricchiazzi and Canfield (1983, Astrophys. J., 272, 739, RC). Model F2 reproduces the peak intensity of the unreversed Mg ii k profile at flare maximum but does not account for high wing intensities. On the other hand, the RC models show the sensitivity of Mg ii line intensities to various electronbeam parameters. Our simulations also show that the microturbulence produces a broader line core, while the intense line wings are caused by an enhanced line source function.

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Section: Synthetic Spectramentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Mg ii Lines Observed During the X-class Flare on 29 March 2014 by the Interface Region Imaging Spectrograph

Liu¹,

Heinzel²,

Kleint³

et al. 2016

Solar and Stellar Flares

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show abstract

“…In CHIANTI software it is necessary to provide the differential emission measure (DEM) and chemical abundances. At first, we calculated DEMs based on semiempirical flare model atmospheres F1 and F2 (Machado et al 1980). Then we used abundances of silicon from Sylwester et al (2015), determined from RESIK crystal spectrometer data.…”

Section: Modeling Of the Uv Emission Of The Solar Flare And Preliminamentioning

confidence: 99%

Observations and modeling of the ultraviolet emission of solar flares

2015

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Abstract. In this paper we present the method of using far UV spectra of the flare observed by Interface Region Imaging Spectrograph (IRIS) for determination of the contribution of the continuum emission to the total UV radiation observed e.g. by SDO in 1600Å channel. In our method the Si IV (1402.77Å) line observed by IRIS is used as a proxy of C IV line emission contained in SDO/AIA UV images. Determined intensity of the flare continuum emission can be used to study the physics of the flare heated chromosphere and for better understanding of the emission mechanisms.

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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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Semiempirical models of chromospheric flare regions

Cited by 260 publications

References 0 publications

Mg ii Lines Observed During the X-class Flare on 29 March 2014 by the Interface Region Imaging Spectrograph

Mg ii Lines Observed During the X-class Flare on 29 March 2014 by the Interface Region Imaging Spectrograph

Observations and modeling of the ultraviolet emission of solar flares

Radiation Hydrodynamics in Solar Flares

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