INTERPLANETARY SHOCKS LACKING TYPE II RADIO BURSTS

Abstract

We report on the radio-emission characteristics of 222 interplanetary (IP)\nshocks. A surprisingly large fraction of the IP shocks (~34%) is radio quiet\n(i.e., the shocks lacked type II radio bursts). The CMEs associated with the RQ\nshocks are generally slow (average speed ~535 km/s) and only ~40% of the CMEs\nwere halos. The corresponding numbers for CMEs associated with radio loud (RL)\nshocks are 1237 km/s and 72%, respectively. The RQ shocks are also accompanied\nby lower peak soft X-ray flux. CMEs associated with RQ (RL) shocks are\ngenerally accelerating (decelerating). The kinematics of CMEs associated with\nthe km type II bursts is similar to those of RQ shocks, except that the former\nare slightly more energetic. Comparison of the shock The RQ shocks seem to be\nmostly subcritical and quasi-perpendicular. The radio-quietness is predominant\nin the rise phase and decreases through the maximum and declining phases of\nsolar cycle 23. The solar sources of the shock-driving CMEs follow the sunspot\nbutterfly diagram, consistent with the higher-energy requirement for driving\nshocks.\n