Characteristics of coronal mass ejections associated with solar frontside and backside metric type II bursts

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We compare fast (υ ≥ 500 km s−1) coronal mass ejections (CME's) with reported metric type II bursts to study the properties of CME's associated with coronal shocks. We confirm an earlier report of fast frontside CME's with no associated metric type II bursts and calculate that 33±15% of all fast frontside CME's are not associated with such bursts. Faster CME's are more likely to be associated with type II bursts, as expected from the hypothesis of piston‐driven shocks. However, CME brightness and associated peak 3‐cm burst intensity are also important factors, as might be inferred from the Wagner and MacQueen (1983) view of type II shocks decoupled from associated CME's. We use the equal visibility of solar frontside and backside CME's to deduce the observability of backside type II bursts. We calculate that 23±7% of all backside type II bursts associated with fast CME's can be observed at the earth and that 13±4% of all type II bursts originate in backside flares. CME speed again is the most important factor in the observability of backside type II bursts.