Instability of the Whistler Structure of Oblique Hydromagnetic Shocks

The characteristic whistler structure of oblique hydromagnetic shocks is observed experimentally to suffer from a rapidly growing short-wavelength instability, which is tentatively identified as the decay instability first predicted by Galeev and Karpman. It is suggested that this instability is responsible for the turbulent whistler shock structure observed when a super-Alfv\'enic plasma stream encounters a magnetic obstacle.