Remote radio tracking of interplanetary CMEs

Two examples of type II radio emissions associated with the propagation of Earth-directed CMEs through the interplanetary medium are illustrated and compared. The two type II radio events were observed by Wind/WAVES in January and May of 1997 and exhibit very different radio characteristics. The analyses presented here use the novel approach of presenting the radio data as a function of the inverse of the frequency and time, which facilitates remote radio tracking of the CME through the interplanetary medium. We demonstrate unequivocally that for the May, 1997 event the radio emissions were generated at the fundamental and harmonic of the plasma frequency in the ambient plasma upstream of the CME-driven shock. For the January, 1997 event we present evidence that some of the radio emissions were generated while the CME-driven shock passed through a CIR. This is the first time that type II radio emissions have been shown to originate in a specific interplanetary structure.