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Understanding solar flares from optical observations Heinzel, P. 2003, Adv. Space Res. 32, 2393. S. Kamio Solar seminar 2004.07.05. Brief summary. This is a review on the behavior of chromosphere during the impulsive phase of flares, mainly from theoretical aspect.
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Understanding solar flaresfrom optical observationsHeinzel, P. 2003, Adv. Space Res. 32, 2393 S. Kamio Solar seminar 2004.07.05
Brief summary • This is a review on the behavior of chromosphere 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
H-alpha • H-alpha emission in the flare is the responses to particle beams. Kasparova and Heinzel (2002) Line profile depends on the height of maximum energy deposition core wing
Fast fluctuations • H-alpha fluctuation is correlated with HXRDennis et al.(1987)Kundu et al.(1989)Rolli et al.(1998)Asai et al.(2002) Correlation of subsecond fluctuations has not yet been established.
Modeling • Non-thermal emission can be modeled with statistical-equilibrium, neglecting dynamics. 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)
RHD simulation • Fisher et al.(1985)Chromospheric evaporation depends on energy flux • Heating ~ radiation • Gentle upflow Heating >> radiation Explosive evaporation Up and down flows Velocity reverse above flare transition region height
up Return current down Electron beams penetrate into high resistivity plasmacurrent heatingenergy deposit in higher atmosphere • Karlicky and Henoux (1992)Strong heating in upper transition regionBut the flow is highly transient
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) Corona Explosive evaporation Chromosphere
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)
Interpretation • Emission in the red wing is absorbed 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
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
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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