Fragmented structure of interplanetary type II bursts

We present the Ulysses observations of a highly fragmented interplanetary t ype II burst and an associated pair of forward shocks. We argue that the co upling of Langmuir waves excited by one of these shocks with escaping radia tion at the sharp density gradient associated with the companion shock is r esponsible for the clumpiness of the type II event. This linear coupling pr ocess is shown to cause large fluctuations in the efficiency of conversion of Langmuir waves into elect romagnetic radiation at the fundamental of the electron plasma frequency f(pe), leading to the fragmentary structure of t he type II radio burst.