Today’s Papers

1. Solar Seminar on 2004 April 19 by Ayumi Asai 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…

2. Flare-Related Magnetic Anomaly with a Sign ReversalQiu 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

3. 1. Introduction What is “magnetic anomaly?” • polarity reversal @HXR sources associated with nonthermal beams • strong B (umbrae) • transient phenomena ~a few minutes distortion of measurements due to unusual conditions HXT H MDI Fig. 1b

4. 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

5. 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 saturation > 1000G Fig. 2d

6. Velocity Field Fig. 4 velocity contour downflow < 2km/s not exactly overlap with the areas of the magnetic anomaly upflow downflow

7. 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

8. 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 asymmetry how significantly the change in the line profile would affect the measurements? Do the sign reversal of magnetic polarity (magnetic anomaly) really occur?

9. 3.1. Absorption Profiles red asymmetry line profiles with B=0 velocity ~2km/s measured B simulated B measured v simulated B Fig. 6a Fig. 6b

10. 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

11. 3.3. Centrally Reversed Profiles • centrally reversed profile lower 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

12. 3.4. Summary variety of combinations of line profiles and velocity fields result in the apparent sign reversal convert 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

13. 4. Nonthermal Beam Effect on the Atmosphere HXT /M1-M2-H • energy deposit by nonthermal beam to turn absorption toemission / 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) electron which can reach TMR

14. 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

15. Impulsive and Gradual Nonthermal Emissions in an X-Class FlareQiu 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

16. Impulsive / Gradual Burst Fig. 1 impulsive gradual

17. Evolution of the Flare • HXR sources in gradual phase are also generated by thick-target emissions due to precipitation of nonthermal particles Fig. 2

18. Footpoint Motion • support successive magnetic reconnection Fig. 4

19. Spatially Resolved Index • FP A and FP C shows the same spectral evolution • These are “conjugate footpoints”

20. Gradual Hard Flare gradual hardening • difference of spectral and light curve evolutions different acceleration mechanism in impulsive/gradual phases

21. Spectral Evolution optically thin optically thick Fig. 5a microwave data : Owens Valley Solar Array • spectral evolution in microwave • optically thick in impulsive phase • optically thin in gradual phase

22. 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

23. Downflow at Flare Ribbons • 2001 April 10 Flare • DST multi-wavelength observation • Ha: -5.0, -1.5, -0.8, -0.4, center, +0.4, +0.8, +1.5 • spatially resolved red asymmetry

24. Red Asymmetry • chromospheric condensation due to rapid pressure enhancement • precipitation of nonthermal particle and thermal conduction front l

25. Dopplergram I

26. 2001 April 10 Flare -1.5 A +1.5 A

27. Dopplergram II

28. Scatter Plot bright dark bright in red bright in blue