Lower Hybrid Waves at Comet 67P
Abstract
Lower hybrid waves are important since they can interact with both ions and electrons, can transfer energy between particle populations, and can reshape the plasma environment of a comet. We investigate the generation of waves observed in the lower hybrid frequency range by observed density gradients in the near plasma environment of comet 67P. When the plasma is dominated by water ions from the comet, a situation with magnetized electrons and unmagnetized ions is favourable for the generation of lower hybrid waves. We consider cometocentric distances out to a few hundred km. We find that when the electron motion is not significantly interrupted by collisions with neutrals, large average gradients within tens of km of the comet, as well as often observed local large density gradients at larger distances, are often likely to be favourable for the generation of lower hybrid waves. Overall, we find that waves in the lower hybrid frequency range are likely to be common in the near plasma environment. We compare generation mechanisms and waves at comet 67P (observed by Rosetta) with observations in the magnetotail (Cluster) and at the magnetopause (MMS).