Understanding solar flaresfrom optical observations

Heinzel, P. 2003, Adv. Space Res. 32, 2393

S. KamioSolar seminar 2004.07.05

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

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

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.

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)

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

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

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

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 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

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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