A Slow Shock Structure Associated with Magnetic Reconnection
in Coronal Mass Ejection

D. Shiota (Kyoto Univ.), H. Isobe, P.F. Chen, and K. Shibata

   Coronal mass ejections (CMEs) are one of the most interesting 
phenomena in the solar corona. The physical processes of CMEs, 
such as energy storage, initiation, evolution, and so on, still 
remain unclear. Recent observations revealed that CMEs are associated 
with either solar flares or giant arcades, in which magnetic 
reconnection is thought to play an essential role. We suppose that 
reconnection also plays an essential role in CMEs. 
   In order to look for evidence of reconnection and study the role of 
reconnection in the evolution of CMEs, we performed magnetohydrodynamic 
simulations of CMEs with magnetic reconnection, and compare the 
numerical results with observations of CMEs and associated phenomena. 
   We found that slow shocks associated with reconnection form a 
Y-shaped structure. Similar Y-shaped structure was observed with 
the Yohkoh Soft X-ray Telescope in a giant arcade formation 
event. By comparison between the numerical results and observational 
data, we conclude that the observed Y-shaped structure corresponds 
to the slow shocks associated with magnetic reconnection.
   We also found that 'dimming', that are associated with CMEs, 
are caused by three processes: expansion of magnetic loop, expansion 
of flux rope (core), and rarefaction by the reconnection inflow.