Magnetic pulses with durations near the local proton cyclotron period: Comet Giacobini-Zinner

Magnetic pulses with durations near the local proton cyclotron period (in the spacecraft frame) have been detected during the ICE encounter with comet Giacobini-Zinner. The pulses typically last only a single cycle (solitary wave), are transverse, noncompressional oscillations, and have peak-to-peak transverse amplitudes of 2-3 nT. Occasional large pulses with amplitudes of 5-7 nT have been detected. The waves typically propagate at angles 2°-15° relative to B₀ and are highly elliptically (linearly) polarized. The pulses have been detected when α, the angle between the ambient magnetic field and the solar wind velocity, is 90°+/-30° and when ICE was 350,000-700,000 km from the comet. At the present time it is uncertain whether such pulses are generated exclusively under large α conditions or whether the presence of large-amplitude heavy ion cyclotron waves during more moderate α conditions mask their presence. It is also unclear whether these pulses are superposed on top of cometary turbulence of simply a part of it. The above observations will be compared to recent theoretical predictions of cometary waves generated during large α conditions.