1

THE RELATION BETWEEN CORONAL EITWAVE AND MAGNETIC CONFIGURATION

Speakers: Xin Chen

23/4/22

23/4/22 2

1. INTRODUCTION

Coronal extrapolated magnetic fields

EIT wave

The relation of CME and EIT wave (mechanism)

23/4/22 3

1.1 Coronal extrapolated magnetic fields

The magnetic features of lower coronal is the key of understanding its physical origins

The direct measurement (Zeeman Splitting) of the coronal magnetic field is particularly difficult

A complementary method of the field measurements is a precise extrapolation of the accurately observed photospheric magnetic field.

Currently potential field approximations can be easily used

1. INTRODUCTION

23/4/22 4

1.2 EIT Wave

Running-difference

1. INTRODUCTION

23/4/22 5

1.2 EIT wave

EIT waves were discovered by the EUV Imaging Telescope (EIT)

They propagate nearly circularly from a flare site (Moses et al. 1997; Thompson et al. 1998) or inhomogeneously, avoiding strong magnetic features and neutral lines. Generally, they stop near coronal holes (Thompson et al. 1999). Research (Biesecker et al. 2002) indicates that if an EIT wave is observed, then there must be a CME. However not all CMEs have associated EIT waves.

The typical velocity of EIT wave is 170~350km/s, average is 270km/s

Generally considered, the brightening and dimming of EIT wave is caused by the increase or decrease of density of plasma in coronal. Some article also indicate variation of temperature is not negligible.

1. INTRODUCTION

23/4/22 6

1.3 The relation of CME and EIT wave (mechanism)

Solar coronal mass ejections (CMEs) are presently the largest known solar eruptive activity in spatial scale. From Visible coronagraph it presents as a transient coronal phenomenon obvious brightening than background .

1. INTRODUCTION

23/4/22 7

1.3 The relation of CME and EIT wave (mechanism)

Fast-mode waves can not explain those properties of EIT wave: The velocity of EIT wave is less than 1/3 velocity of Moreton wave Delanne´e & Aulanier discover sometimes EIT wave would stop at

magnetic separator surface The velocity of EIT wave has no correlation with velocity of type II

radio bursts at the same time, however the velocity of Moreton wave is proportional to the latter

The wave velocity of EIT wave sometimes is much smaller than lower coronal sound speed, since the fast-mode waves are always larger than it

1. INTRODUCTION

23/4/22 8

1.3 The relation of CME and EIT wave (mechanism)

Numerical simulation result from Chen, P.F.:Global evolution of the density (color), magnetic field (solid lines), and velocity (arrows).

1. INTRODUCTION

23/4/22 9

1.3 The relation of CME and EIT wave (mechanism)

Evolution of the density (r) distribution. Note that the r distribution at each time is stacked on the previous one.

1. INTRODUCTION

23/4/22 10

1.3 The relation of CME and EIT wave (mechanism)

Propagation of EIT wave front from point C to point D, where the rising flux rope is the original source for the successive opening of all field lines. Solid lines represent the initial configuration; dashed lines correspond to the new configuration at each new time; wavy lines represent the fast-mode waves emitted from the EIT wave fronts. Moreton waves, much ahead of the EIT wave fronts, are not shown.

1. INTRODUCTION

23/4/22 11

2. DATA PROCESSING

2.1 PFSSThe coronal magnetic field models used from IDL – SSW – PFSS. This software is based on evolving full-sun Carrington maps of the photospheric magnetic field, into whichSOHO/MDI magnetograms are directly inserted when available. The coronal magnetic field is then deduced by extrapolating the photospheric field upward via the potential-field source-surface (PFSS) approximation.

23/4/22 12

2.1 PFSS

Since MDI magnetograms is a synthesis of one rotation cycle of sun (27 days), PFSS can not show the variation of magnetic field when EIT wave arising (1-2 hours). All extrapolated magnetic field lines present the quiet sun magnetic structure before EIT wave.

2. DATA PROCESSING

23/4/22 13

2.2 Running-difference& Base-differenceIn running-difference, brightening/dimming show the variation of the last recent data. If changing it to minus the data before EIT wave begins, in other words, comparing with the quiet sun. We got base-difference, which is appropriate to analyze the density variation of plasma.

2. DATA PROCESSING

23/4/22 14

2.3 Combine the PFSS extrapolated magnetic field lines and EIT wave

The magnetic field lines in left picture present the quiet sun magnetic field, it does not change. Only the background of EIT base-difference will vary with time.

*footpoints chosen from isometric lon-lat grid

2. DATA PROCESSING

23/4/22 15

3. RESULTS

EIT wave in 04-07-1997

(1)

(2)

(3)

23/4/22 16

EIT wave in 04-07-1997 (1)

23/4/22 17

EIT wave in 04-07-1997 (2)

23/4/22 18

EIT wave in 04-07-1997 (3)

23/4/22 19

(1)

(3)

(2)

(4)

EIT wave in 05-12-1997

23/4/22 20

EIT wave in 05-12-1997 (1)

23/4/22 21

EIT wave in 05-12-1997 (2)

23/4/22 22

EIT wave in 05-12-1997 (3)

23/4/22 23

EIT wave in 05-12-1997 (4)

23/4/22 24

(1)

(3)

(2)

(4)

EIT wave in 04-29-1998

23/4/22 25

EIT wave in 04-29-1998 (1)

23/4/22 26

EIT wave in 04-29-1998 (2)

23/4/22 27

EIT wave in 04-29-1998 (3)

23/4/22 28

EIT wave in 04-29-1998 (4)

23/4/22 29

4. CONCLUSION

This method ---- comparison of full-disk extrapolation magnetic field with EIT base-difference as background is accordant with previous researching conclusion.

According to the mechanism from Chen, P. F. et al 2002. It can explain:

1.EIT wave avoiding strong magnetic features and neutral lines

2.The rotation of brightening of EIT wave

23/4/22 30

4. CONCLUSION

Method: Comparison PFSS full-disk extrapolation magnetic field with EIT base difference

Example: Analyze 3 major EIT events during 1997-1998

Test: Present the properties of EIT wave

Mechanism: EIT wave stretch closed field lines driven by an erupting flux rope.