UNUSUAL WAVE PHENOMENA NEAR INTERPLANETARY SHOCKS AT HIGH-LATITUDES

We report on several interplanetary shocks that are unusual because wa ves at about 10 Hz are highly electrostatic in the upstream region yet highly electromagnetic in the downstream region. These shocks, detect ed by the Unified Radio and Plasma Wave Experiment (URAP) on Ulysses a re supercritical reverse shocks, which occurred predominantly at high heliographic latitudes. The level of wave activity is observed to be i ndependent of the angle between the magnetic field and the shock norma l, the Mach number, and the change in the ratio of ion thermal pressur e to magnetic pressure from upstream to downstream regions. Since the energy in the upstream electrostatic waves is small compared to the do wnstream electromagnetic waves, mode conversion from electrostatic to electromagnetic at the shock is not a viable mechanism. The upstream a nd downstream waves are likely to be generated by separate mechanisms, with lower hybrid waves being the most probable candidates for the up stream waves and electromagnetic lower hybrid or whistlers for the dow nstream waves.