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 ~15% of the interplanetary shocks, (2) occur mostly in the upstream regions, and (3) are produced in the vicinity of both quasi-parallel Q || and quasi-perpendicular Q ⊥ shocks and that (4) Langmuir wave-producing shocks are supercritical. Since Langmuir waves are the essential ingredients for the solar and interplanetary type II burst excitation, these observations imply that (1) the shock responsible for type II emission can be either Q || with a shock normal angle, θ B , n ≤ π/4, or Q ⊥ with θ B , n > π/4, (2) type II bursts are excited in the upstream regions, (3) the θ B , n need not be close to ~π/2 for either the excitation or the clumpiness of the type II bursts, and (4) type II shocks are mostly supercritical.