Influence of coronal mass ejection interaction on propagation of interplanetary shocks

We studied 91 interplanetary (IP) shocks associated with coronal mass ejections (CMEs) originating within about +/-30degrees in longitude and latitude from the center of the Sun during 1997-2002. These CMEs cover a wide range of initial speeds of about 120 to 2400 kms(-1) and they also include a special population of 25 interacting CMEs. This study provides the characteristics of propagation effects of more number of high-speed CMEs (V-CME > 1500 kms(-1)) than the data used in earlier studies. It enables to extend the shock-arrival prediction model to high-speed CMEs. The results on comparison of IP shock speed and transit time at 1 AU suggest that the shock transit time is not controlled by its final speed but is primarily determined by the initial speed of the CME and effects encountered by it during the propagation. It is found that the CME interaction tends to slow the shock and associated CME. The deviations of shock arrival times from the empirical model are considerably large for slow (V-CME < 300 kms(-1)) and fast (V-CME > 800 kms(-1)) CMEs. Results show that the slow and fast CMEs experience stronger effective acceleration.