1. Fast Magnetosonic Waves and Global Coronal Seismology in the Extended Solar Corona
Ryun Young Kwon, Jie Zhang, Maxim Kramar, Tongjiang Wang, Leon Ofman, & Joseph M. Davila

2. Contents Finding: Fast magnetosonic waves in the extended solar corona
Application: Global coronal seismology
I wanna show today global coronal seismology, to determine magnetic field strengths in the extended solar corona, using traveling fast magnetosonic waves.
My talk consists of two parts.
The first, I’m gonna introduce new observations of fast magnetosonic waves, traveling in the extended solar corona, observed by STEREO COR1 coronagraphs.
And I’m gonna prove that the traveling disturbance is in fact fast magnetosonic waves.
Than, I’ll discuss the results.

3. Introduction Fast magnetosonic waves associated with flares/CMEs
Moreton waves (Moreton 1960), EUV waves (Thompson et al. 1999), and type II radio bursts (Wagner & MacQueen 1983)
Reasons for controversies: unknown physical parameters, especially, magnetic field strengths -> local fast mode (Alfvén) speed
Previous coronal seismology
Localized magnetic structures (e.g., coronal loops; Aschwanden et al. 1999)
A specific coronal layer (e.g., EUV wave; Ballai 2007)
Radial or nearly radial direction (e.g., type II radio burst and shock ahead of CME leading edge; Vršnak et al. 2002; Gopalswamy & Yashiro 2011)
PFSS models: Neglected plasma structures.
Global coronal seismology in the extended solar corona for comprehensive understanding of various aspects of fast magnetosonic waves
Associated with flares/CMEs, fast magnetosonic waves may be triggered to propagate into the solar coronal medium and they may be observed in the form of Moreton waves, EUV waves, and type II radio bursts.
However, it has been highly debated whether or not that they are truly fast magnetosonic waves.
The most important reason for … we have no idea what’s going on in the corona.
In order to overcome…
Note that the fast mode waves are global phenomena, traveling across magnetized plasma structures.
So, in order to interpret the observed signatures of fast mode waves, we should understand global distributions of magnetic field strengths.

4. Fast magnetosonic wave vs. Magnetic reconguration scenario
Imaging observations of coronal fast magnetosonic waves: EUV waves
The first thing, we have to find true waves to apply for global coronal seismology.
I wanna remind you there is a still a debate on the nature of EUV waves.
In general, it’s hard to know whether or not that the observed fronts are true wave fronts or not.
This movies show EUV waves observed by two STEREO spacecrafts, supporting that the EUV waves are in fact fast mode waves
 Patsourakos &Vourlidas, Angelos 2009

5. Alternative interpretation (Schrijver et al. 2011)
There exists an alternative interpretations.
They pointed out that the global magnetic field configuration is very imporant.
It can be observed a freely propagating front separated from CME body.
These scenarios are highly supported by an observational characteristics of EUV waves, this is stationary fronts.
It is well know that propagating EUV waves stop..
Separation from flux rope (current shell or overlying magnetic field lines)
Stop at separatrices (boundaries of coronal holes) -> stationary fronts
Constraint: Streamers (global separatrices)

6. White-light wave
Kwon et al. (2013, ApJ, 766, 55)

7. Time-distance maps

8. Global coronal seismology
Fast magnetosonic speed,
Alfvén speed,
Sound sped,
Magnetic field are parallel to each other and wave vectors are perpendicular to the magnetic field lines,
Magnetic field strength in cgs unit,

9. Radial profiles
Speeds of white light wave are in fact local fast magnetosonic speeds!
Saito et al. (1977)

10. Physical implications: EUV waves
EUV waves would be refracted toward upper corona or lower chromosphere corona and disappear.

11. Side view
Top view
Low coronal layer
EIT waves are signatures of downward fast magnetosonic waves refracted from the upper solar corona, as the same as an interpretation of Moreton waves (Uchida 1968), rather than freely propagating fast magnetosonic wave in a certain coronal layer.

12. Physical Implications
Correlation between fast magnetosonic speed and magnetic field strength
Yang & Chen (2010) found that speeds of EUV waves have significant negative correlation with magnetic field strengths determined with a potential field model.
Correlation coefficients of fast magnetosonic speed
Electron density (ne-1/2): 0.61
Magnetic field strength: -0.02
Electron density is important! (not modeled magnetic field)
Discrepancy of speeds between EUV waves and type II radio bursts (Klassen et al. 2000)
Increasing fast magnetosonic speed with height: 465km s−1 (EUV wave), 829 to 1723 km s−1 (White light wave at 1.6 – 3.0 Rs)
Type II radio bursts are shock signatures in the upper corona

13. Summary
High time cadence white-light observations: STEREO SECCHI COR1 coronagraphs
White light waves
Global coronal seismology (magnetic field strengths in a wide spatial range of the extended solar corona)
Interpretations of various manifestations of fast magnetosonic waves
Moreton waves and EUV waves
EUV waves vs. type II radio bursts

14. Thank you!!