Today’s Papers 1. Flare-Related Magnetic Anomaly with a Sign Reversal Jiong Qiu and Dale E. Gary,...

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