Fast Shock Formation in the Subsonic Magnetic Reconnection 

T. Shimizu (Ehime Univ.) and M. Ugai

The subsonic magnetic reconnection in the closed boundary system was studied in MHD simulations. 
When the upstream field region is high beta (i.e. > 0.5), the reconnection jet is subsonic. 
Nevertheless, the jet can be temporally supersonic, i.e. superfast, in the stationary frame, 
when the jet region is sufficiently long. 
This is caused by the plasmoid (plasma loop) propagation. 
The fast shock is much weaker than that of supersonic magnetic reconnection. 
The differences between the supersonic and subsonic reconnections are discussed.