A Numerical Model of a Coronal Mass Ejection Shock Development

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					  A Numerical Model of a Coronal Mass
                 Ejection:
Shock Development with Implications for the
       Acceleration of GeV Protons

    Roussev, I.I., Sokolov, I.V., Forbes, T.G.,
     Gombosi, T.I., Lee, M.A. and Sakai J.I.
              ApJ, 2004, 605, 73L

          Taiyou Zasshikai on May 17, 2004
                   Daikou Shiota
                     Introduction
Coronal mass ejection (CME)
                                      Major hazard for spacecraft
Solar energetic particle (SEP) events
High energy protons (100MeV) are particularly important
It has been proposed (e.g., Lee 1997; Reames 1999) these particles
are produced by a Fermi process (type A) at a shock in front of the
CME (close to the Sun ~10Rsun).
However, whether or not such a process is actually feasible has
remained uncertain (Tsurutani 2003), because of the lack of
knowledge about strength and location of the shock.
             Initial configuration
Magnetogram data of AR8210 (Wilcox Solar Observatory)
Composite synoptic map (Carrington maps for rotation 1935 &
1936)    during the period from April through May of 1998
    the potential field source surface method
        (PFSSM; Altschuler et al. 1977)
3D magnetic field
 + empirical model (Roussev et al. 2003)
        ↓ time evolution
        a steady state solar wind
Magnetic configuration and flow pattern
               Initiation of CME
         (Amari et al. 1999, 2000, 2003)




shear motions   horizontal boundary motions   converging
                                              motions
Movie
                Fast-wave speed




Because of this sharp decrease so close to the Sun, the velocity
of the ejecta quickly becomes supersonic.
        Speed & Trajectories of the flux rope
                  and the shock




t<220
pure shear
motions                                            t=326-365
                                                   rapid deceleration due
             t=220-326    t=326-365                to the formation of the
             converging   rapid acceleration due   current sheet
             motions      to loss of equilibrium
3D view
       Compression ratio of the shock
         & Proton cut-off energy




a high-energy cutoff for SEPs predicted on the basis of diffusive
shock acceleration
                    Conclusion
• There has been some controversy in recent years about
  whether or not diffusive shock acceleration theory can
  account for the GeV particles observed early in SEP
  events.
• By constructing a fully three-dimensional numerical
  model, which incorporates solar magnetic data and a
  loss-of-equilibrium mechanism, they have been able to
  determine that a shock can develop close to the Sun
  sufficiently strong to account for energetic particles up
  to 10 GeV.

				
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