Alfven wave amplifications and generation at cometary bow shocks

The possible effect of hydromagnetic wave amplification and generation at cometary bow shocks is investigated by means of a planar hydromagnetic shock model. For the inbound crossing of comet Halley's bow shock, it is found that the transmission of the sunward-streaming hydromagnetic waves through the bow shock could lead to the enhancement of its wave amplitude by a factor of 2-3 and the generation of Alfvén waves with the opposite helicity. The plasma observations during inbound crossing of comet Halley's bow shock provide some evidence for such effect.