Numerical studies have been done by J.M. Schmidt and P. J. Cargill of Imperial College, London, UK and the results published in the Annales Geophysicae June 14, 2004.  In their publication they describe the interaction of two shock waves using the interactions of two Coronal Mass Ejections (CMEs). 

Usually these CMEs are travelling at different speeds and the interaction equalizes them.  Both these CMEs have a magnetic orientation which means they either have the same sense or the they are oriented in the opposite sense.    When the CME’s have the opposite sense they combine into a single structure, nonelastically.  If they have the same sense, they become sticky as a result of magnetic reconnection.  In either case these are magnetic space structures that have the form of birds.

Drawing is from Schmidt and Cargill's Article

REFERENCE:

http://www.ann-geophys.net/22/2245/2004/angeo-22-2245-2004.pdf