Observations of interplanetary shocks

A surprisingly large fraction of the IP shocks (~34%) was radio quiet (RQ; i.e., the shocks lacked type II radio bursts). We examined the properties of coronal mass ejections (CMEs) and soft X-ray flares associated with such RQ shocks and compared them with those of the radio-loud (RL) shocks.

The CMEs associated with the RQ shocks were generally slow (average speed ~535km/s) and only ~40% of the CMEs were halos. The corresponding numbers for CMEs associated with RL shocks were 1237km/s and 72%, respectively. Thus, the CME kinetic energy seems to be the deciding factor in the radio-emission properties of shocks.