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Today’s Papers
1. Flare-Related Magnetic Anomaly with a Sign Reversal
Jiong Qiu and Dale E. Gary, 2003, ApJ, 599, 615
2. Impulsive and Gradual Nonthermal Emissions in an X-Class Flare
Jiong Qiu, Jeongwoo Lee, and Dale E. Gary, 2004, ApJ, 603, 335
3. Others…
Solar Seminar on 2004 April 19 by Ayumi Asai
Flare-Related Magnetic Anomaly with a Sign Reversal
Qiu J. and Gary D., 2003, ApJ, 599, 615
• Magnetic anomaly : transient change of magnetic field during a flare (apparent sign reversal of magnetic polarity)
produced by distortion of line as a result of nonthermal beam impact on the atmosphere of the flare region
1. Introduction
What is “magnetic anomaly?”
• polarity reversal @HXR sources
associated with nonthermal beams
• strong B (umbrae)• transient phenomena
~a few minutesdistortion of
measurements due to unusual conditions Fig. 1b
MDI
HXT H
Contents• simulation of the MDI measurements to
understand the role of a modified Ni I line profile in producing the magnetic anomaly
• analysis of the HXR observation to deduce the energy flux deposited at the location of the anomaly
• discussion about the probable mechanisms for the flare-related magnetic anomaly
• effects of saturation and velocity field on MDI measurements
2. Observation of Magnetic Anomaly
• polarity reversal occurs temporally, and resume
• there is no significant change except for flare kernels
• different from saturation (persistent throughout the flare)
failure of the onboard algorithm Fig. 2d
saturation> 1000G
Velocity Field
downflow< 2km/s
Fig. 4 velocity contour
upflowdownflow
not exactly overlap with the areas of the magnetic anomaly
Temporal Correlation with HXR
• close temporal association between magnetic anomaly and the footpoint HXR emissions
• both the timing and the locations of the downflow are not particularly well correlated with magnetic anomaly
Fig. 5
3. MDI Measurements on Changing Line Profiles
• flare-induced line profile changes• no comprehensive treatment of line
formation and radiative transfer• simulated MDI output, by adjusting line
intensity, width, and asymmetryhow significantly the change in the line
profile would affect the measurements?Do the sign reversal of magnetic polarity
(magnetic anomaly) really occur?
3.1. Absorption Profilesline profiles with B=0
velocity ~2km/s
simulated Bmea
sure
d B
simulated Bmea
sure
d v
red asymmetry
Fig. 6a Fig. 6b
3.2. Emission
• in strong-field region (>1500 G), a sign reversal is generated
• with background velocity field, a sign reversal is produced even in weak-field regions
• measured velocity field is also sign-reversed
Fig. 6c
3.3. Centrally Reversed Profiles
• centrally reversed profilelower atmosphere is
predominantly heated• a sign reversal of
measurement depends on the line width and the intensity of central reversal
• with background velocity field, a sign reversal occurs in weak-field regions
Fig. 6e
3.4. Summaryvariety of combinations of line profiles and velocity
fields result in the apparent sign reversalconvert absorption to emission• gap of the sign reversal of velocity field is also
explained significantly broadened line profiles with a strong
central reversal• moderate velocity field would lead to the sign
reversal in weak magnetic field region, and not in strong magnetic field region
information of real velocity field is needed result of nonthermal beam impact
4. Nonthermal Beam Effect on the Atmosphere
HXT /M1-M2-H
electron which can reach TMR
• energy deposit by nonthermal beam to turn absorption to emission / centrally reversed line
• TMR is not directly heated by >350keV electrons
• nonthermal excitation and ionization generate a enhance source function to turn the absorption to emission (Ding et al. 2002)
6. Conclusions
• magnetic anomaly in MDI• correlate with HXR sources, appear at flare
maximum, in umbral regions of strong magnetic field
sign reversal is associated with precipitating nonthermal electrons
• sign reversal is generated when absorption is centrally reversed or comes into emission
• sign reversal may not be produced by direct penetration, but by a comprehensive radiative transfer effect
Impulsive and Gradual Nonthermal Emissions in an X-Class Flare
Qiu J., Lee J., and Gary D., 2004, ApJ, 603, 335
• Comprehensive case study of an X-class (X5.6) flare observed on 2001 April 6
• Spatially resolved features of a gradual hardening flare with HXR and microwave data
Impulsive / Gradual BurstFig. 1impulsive gradual
Evolution of the Flare
• HXR sources in gradual phase are also generated by thick-target emissions due to precipitation of nonthermal particles
Fig. 2
Footpoint Motion
• support successive magnetic reconnection
Fig. 4
Spatially Resolved Index
• FP A and FP C shows the same spectral evolution
• These are “conjugate footpoints”
Gradual Hard Flare
• difference of spectral and light curve evolutions
different acceleration mechanism in impulsive/gradual phases
gradual hardening
Spectral Evolution
microwave data : Owens Valley Solar Array• spectral evolution in microwave• optically thick in impulsive phase• optically thin in gradual phase
optically thick optically thin
Fig. 5a
7. Conclusions
• gradual burst is produced by a physical mechanism different from that for the impulsive components
• both impulsive and gradual HXR sources are thick-target ones
support magnetic reconnection model
Downflow at Flare Ribbons• 2001 April 10 Flare• DST multi-wavelength observation• H: -5.0, -1.5, -0.8, -0.4, center, +0.4, +0.8, +1.5
• spatially resolved red asymmetry
Red Asymmetry
• chromospheric condensation due to rapid pressure enhancement
precipitation of nonthermal particle and thermal conduction front
Dopplergram I
2001 April 10 Flare
+1.5 A-1.5 A
Dopplergram II
Scatter Plot
bright in red bright in blue
bright
dark