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

Abstract

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 masks their presence. It is also unclear whether these pulses are superposed on top of cometary turbulence or simply a part of it. The above observations will be compared to recent theoretical predictions of cometary waves generated during large α conditions.