Download - Understanding solar flares from optical observations Heinzel, P. 2003, Adv. Space Res. 32, 2393
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Understanding solar flaresfrom optical observations
Heinzel, P. 2003, Adv. Space Res. 32, 2393
S. KamioSolar seminar 2004.07.05
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Brief summary• This is a review on the behavior of chromosp
here during the impulsive phase of flares, mainly from theoretical aspect.
•Fast fluctuation of H-alpha and HXR
•Radiative-Hydrodynamical models of flares
•Line asymmetries and flare dynamics
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H-alpha • H-alpha emission in the flare is the responses
to particle beams.
core wing
Kasparova and Heinzel (2002)Line profile depends on the height of maximum energy deposition
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Fast fluctuations• H-alpha fluctuation is correlated with HXR
Dennis et al.(1987)Kundu et al.(1989)Rolli et al.(1998)Asai et al.(2002)
Correlation of subsecond fluctuations has not yet been established.
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Modeling• Non-thermal emission can be modeled with
statistical-equilibrium, neglecting dynamics.
ijijij CRP Radiation Collision
Non-thermal collisional rate
Heinzel(1991)•Electron density variation do not follow temperature•Significant response in H-alpha•H-alpha intensity drop at pulse onset (sub-second)
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RHD simulation• Fisher et al.(1985)
Chromospheric evaporation depends on energy flux
Heating ~ radiationGentle upflowHeating >> radiationExplosive evaporation Up and down flows Velocity reverse above flare transition region
height
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Return currentElectron beams penetrate into hi
gh resistivity plasmacurrent heatingenergy deposit in higher atmosphere
• Karlicky and Henoux (1992)Strong heating in upper transition regionBut the flow is highly transient
down
up
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Red asymmetry• Emission enhancement of the red wing in the
H-alpha line (Ichimoto and Kurokawa,1984)• Caused by downward moving chromospheric
condensation (Canfield and Gayley, 1987)
Explosive evaporation
Chromosphere
Corona
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Blue asymmetry?• Less frequently observed (Heinzel, 1994)
Blue asymmetry is seen at onset of a flare and disappears within a few minutes.Found in centrally reversed line profile (Svestka, 1976)
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Interpretation• Emission in the red wing is ab
sorbed by downward moving plasma.(Heinzel, 1994)
• Down flow in upper chromosphere can produce a blue asymmetry.(Ding and Fang, 1997)
• Blue asymmetry is seen in a special condition
λ λ
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Required optical data• Ideally…
Sub-second temporal variation of spectral line profiles in the whole 2D field of view.
• Currently availableSpectrograph with fast CCD (1D)Multi spectral line dataWavelength scanning of narrow band filter
• Also of noteCollaboration with RHESSIImpact polarization
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Conclusion• Various attempts have been made to derive
the physical condition of the flare atmosphere from optical line observation.
• Detailed comparison of time-dependent RHD simulations with high-resolution spectral observation in optical, IR, UV, EUV, and HXR is needed to understand the flare evolution.
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