Plasma fluctuations and large-scale mixing near comet Giacobini-Zinner

Low-pass filtered data from the ICE electron spectrometer are used to examine relationships between plasma densities, flow speeds, flow directions, and temperatures at distances within approx.105 km of the Comet Giacobini-Zinner nucleus. The sheath/transition region is characterized by electron temperatures of approx.4 x 105 K but with flow speeds and densities that commonly vary by factors of three or more. The largest amplitude density spikes often have significant flow changes associated with them, but a consistent pattern (as might accompany cometary rays, for example) is not found. Power spectral analyses in and near the sheath/transition regions show that density fluctuation levels are enhanced by all detectable frequencies from approx.0 to 21 mHz, consistent with strong density fluctuations on all measured time scales. Marginally significant power peaks are seen at periods of approx.4 min on the inbound pass and at approx.2 min on the outbound pass. Mechanisms such as amplification of convected ion pick-up waves and cometary rays for producing the large plasma variations are discussed. It is also suggested that a Rayleigh-Taylor driven mixing mechanism at a mass loading boundary approx.105 km from the nucleus may be operative