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

Contents

• Finding: Fast magnetosonic waves in the extended solar corona

• Application: Global coronal seismology

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

Fast magnetosonic wave vs. Magnetic reconguration scenario

• Imaging observations of coronal fast magnetosonic waves: EUV waves

Patsourakos &Vourlidas, Angelos 2009

Alternative interpretation (Schrijver et al. 2011)

• Separation from flux rope (current shell or overlying magnetic field lines)• Stop at separatrices (boundaries of coronal holes) -> stationary fronts• Constraint: Streamers (global separatrices)

White-light wave

Kwon et al. (2013, ApJ, 766, 55)

Time-distance maps

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,

222222222cos4

2

1cvcvcvv SASASAf

4/BvA

/PcS

cvv SAf

222

)(4 22Sf cvB

Radial profiles

Saito et al. (1977)

Speeds of white light wave are in fact local fast magnetosonic speeds!

http://en.wikipedia.org/wiki/Seismology

Physical implications: EUV waves

EUV waves would be refracted toward upper corona or lower chromosphere corona and disappear.

22.2 rB

Side view

Top view

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.

Low coronal layer

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

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

Thank you!!