Evolution of Interplanetary Shocks and their CME Drivers

Shock-driving coronal mass ejections (CMEs) constitute the most energetic phenomena in the heliosphere. The shocks can be identified in a number of ways based on remote-sensing and in situ observations. Type II radio bursts are the earliest indicators of shocks that accelerate electrons to energies up to -10 keV. Solar energetic particle (SEP) events are always accompanied by long wavelength type II bursts indicating that the same shock accelerates ions and electrons. A recent investigation involving a large number of interplanetary (IP) shocks revealed that about 35% of them do not produce type II bursts (radio quiet, RQ) or SEPs. Comparison of the RQ shocks with the radio loud (RL) ones revealed some interesting results such as: (1) the lack of evidence for blast waves,(2) energetic particle enhancement in the shock front in -20% of RQ shocks, and (3) determination of the difference between the RQ and RL shocks in terms of the different kinematic properties of the associated CMEs. On the other hand the shock properties measured at I AU are not too different for the RQ and RL cases. This can be attributed to the interaction with the IP medium, which seems to erase the difference. Implications of this evolution for the geoeffectiveness is also discussed.