  Proton mirror modes are large amplitude nonpropagating structures frequently
observed in the magnetosheath. It has been suggested that electron temperature
anisotropy can enhance the proton mirror instability growth rate while leaving
the proton cyclotron instability largely unaffected, therefore causing the
proton mirror instability to dominate the proton cyclotron instability in
Earth's magnetosheath. Here, we use particle-in-cell simulations to investigate
the electron temperature anisotropy effects on proton mirror instability
evolution. Contrary to the hypothesis, electron temperature anisotropy leads to
excitement of the electron whistler instability. Our results show that the
electron whistler instability grows much faster than the proton mirror
instability and quickly consumes the electron free energy, so that there is no
electron temperature anisotropy left to significantly impact the evolution of
the proton mirror instability.
