Hydromagnetic waves associated with cometary water group ions: Sakigake observation
Long-period hydromagnetic waves near the local “water group” ion cyclotron frequency were detected at the closest approach of Sakigake to comet P/Halley. These transverse waves having ~ 2nT peak-to-peak amplitude propagated approximately parallel to the ambient field. The necessary cometary pickup-ion density of “water group” ions for excitation of these waves at 7 106 km upstream from the comet can be inferred to be of the order of 10−3cm−3.
Key wordsHM wave water group ions
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