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 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.

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.

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

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)

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,

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

Physical implications: EUV waves EUV waves would be refracted toward upper corona or lower chromosphere corona and disappear. http://en.wikipedia.org/wiki/Seismology

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.

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!!