On the nature of EIT waves, EUV dimmings and their link to CMEs

A. N. Zhukov and F. Auchère

A&A 427, 705–716 (2004)

Abstract

EIT wave and EUV dimming frequently accompany CME

EIT wave in the Fe XV (284A) EIT wave is a purely coronal phenomenon that does not propagate in the transition region plasma.

EIT wave can be regarded as a bimodal phenomenon. wave mode & eruptive mode

CME mass observed by the EIT is estimated to be about 1015 g. 50% of CME mass is contained outside of transient coronal hole.

Introduction

EIT wave (195 A) strongly associated with CMEs

propagating bright front

propagates nearly isotropically and often globally

stopping at the boundaries of coronal holes

propagation speed is typically 250 km/s

MHD wave?fast mode? ≠ 1000 km/s in low slow mode? ≠ propagates nearly isotropically

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Introduction

EUV dimming EUV dimming is usually observed behind an EIT wave

often the dimming appears as a transient coronal hole

dimming are due to the evacuation of mass during the CME

Sometimes dimmings occur ahead of the EIT wave bright front

situated at the distant footpoints of these large-scale loops overlying the erupting active region.

The bright front (EIT wave) appears due to the plasma compression in the process of successive opening of magnetic field lines during the CME lift-off.

EIT waves are not “real” magnetohydrodynamic (MHD) waves.

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EIT waves observed in different parts ofthe solar spectrum

Moreton wave (H) 800 – 1000 km/s, up to distance of 5×105 km

usually decelerate down to speeds in the range of 200 – 650 km/s

identified as the intersections of a coronal MHD fast-mode shock front and the chromosphere

TRACE wave registered in 195 A (corona, strong) and 171 A (corona + TR, weak)

the EIT wave is a coronal phenomenon and does not propagate in the transition region.

not in Ly (1216 A, chromosphere)

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EIT waves observed in different parts ofthe solar spectrum22

EIT wave observed in the Fe XV (284 A)

EIT waves observed in different parts ofthe solar spectrum22

EIT wave observed in the Fe XV (284 A)

EIT waves observed in different parts ofthe solar spectrum22

behind the front (50 km/s)

ahead of the front (300 km/s)

ahead of the front (300 km/s)

ahead of the front

EIT wave observed in the Fe XV (284 A, corona + upper TR)

dominate by the network structure

EIT wave does not propagate in the upper transition region, but only in the corona.

Dimmings trace the opening of the magnetic field line.

Bimodality of EIT wave33EIT wave observed on May 21 – 22, 2002

Bimodality of EIT wave

eruptive mode :the propagation of a dimming (and a bright front ahead of it) as a result of successive opening of magnetic field lines with lifting of the coronal plasma along these new quasi-open field lines.

The bright front (EIT wave) represents compression of the loops. (“em” : 60 km/s)

“wm” : 250 km/s

33EIT wave observed on May 21 – 22, 2002

Bimodality of EIT wave33EIT wave observed on May 27, 2000

Bimodality of EIT wave

wave mode :The existence of the wave mode is evidenced by the absence of pronounced dimmings at the farthest locations reached by the EIT wave. (300 200 km/s)

33EIT wave observed on May 27, 2000

Transient coronal holes and CME mass44

TCH Dimming<

1 : inside the TCH and dimming

2: outside the TCH but inside the dimming

Transient coronal holes and CME mass44

eruption form the TCH : 7×1014 g eruption form the whole dimming region (including TCH) : 1.4×1015 g lower limit of the true CME mass : 4.2×1015 g

inside the TCH outside the TCH

Discussion and conclusion

EIT wave can be regarded as a bimodal phenomenon. wave mode & eruptive mode

It is still not clear if EIT waves represent real MHD waves or if they rather result from successive opening of the magnetic field line.

CME mass observed by the EIT is estimated to be about 1015 g. 50% of CME mass is contained outside of transient coronal hole.

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