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Geophysical Research Letters

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

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Abstract

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 ∼105 km of the Comet Giacobini-Zinner nucleus. The sheath/transition region is characterized by electron temperatures of ∼4 × 105K 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 at all detectable frequencies from ∼0 to 21 mHz, consistent with strong density fluctuations on all measured time scales. Marginally significant power peaks are seen at periods of ∼4 min on the inbound pass and at ∼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 ∼105 km from the nucleus may be operative.

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