1. 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)

2. 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.

3. 1 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 b slow mode? ≠ propagates nearly isotropically

4. 1 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.

5. EIT waves observed in different parts of the solar spectrum2
Moreton wave (Ha)
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 Lya (1216 A, chromosphere)

6. EIT waves observed in different parts of the solar spectrum2
EIT wave observed in the Fe XV (284 A)

7. EIT waves observed in different parts of the solar spectrum2
EIT wave observed in the Fe XV (284 A)

8. EIT waves observed in different parts of the solar spectrum2
EIT wave observed in the Fe XV (284 A, corona + upper TR)
ahead of the front (300 km/s)
dominate by the network structure
behind the front (50 km/s)
ahead of the front (300 km/s)
Dimmings trace the opening of the magnetic field line.
EIT wave does not propagate in the upper transition region, but only in the corona.
ahead of the front

9. Bimodality of EIT wave 3
EIT wave observed on May 21 – 22, 2002

10. Bimodality of EIT wave 3
EIT wave observed on May 21 – 22, 2002
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

11. Bimodality of EIT wave 3
EIT wave observed on May 27, 2000

12. Bimodality of EIT wave 3
EIT wave observed on May 27, 2000
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)

13. Transient coronal holes and CME mass4
TCH
<
Dimming
1 : inside the TCH and dimming
2: outside the TCH but inside the dimming

14. Transient coronal holes and CME mass4
inside the TCH outside the TCH
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

15. Discussion and conclusion5
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.