Langmuir waves in the vicinity of interplanetary shocks and the consequences for type II burst models

The in situ wave data obtained by the Ulysses Unified Radio And Plasma wave experiment in the vicinity of a large number of interplanetary shocks show that Langmuir waves (1) are observed in only similar to 15% of the interpl anetary shocks, (2) occur mostly in the upstream regions, and (3) are produ ced in the vicinity of both quasi-parallel Q(parallel to) and quasi-perpend icular Q(perpendicular to) shocks and that (4) Langmuir wave-producing shoc ks are supercritical. Since Langmuir waves are the essential ingredients fo r the solar and interplanetary type II burst excitation, these observations imply that (1) the shock responsible for type II emission can be either el l with a shock normal angle, theta (B,n) less than or equal to pi /4, or Q( perpendicular to) with theta (B,n) > pi /4, (2) type II bursts are excited in the upstream regions, (3) the theta (B,n) need not be close to similar t o pi /2 for either the excitation or the clumpiness of the type II bursts, and (4) type II shocks are mostly supercritical.