Reply to comment by Remya et al. on “Effects of electron temperature anisotropy on proton mirror instability evolution”

Abstract

AbstractIn the comment to our paper, Remya et al. (2017) state that we conclude that their theory is incorrect; however, no such conclusion is in our paper. In fact, as stated in their paper, we agree with their theory that shows the impact of heavy ions and electron temperature anisotropy on the competition of the ion anisotropy instabilities. While their linear theory is correct, our paper focused on the nonlinear evolution, where one needs to be careful in assuming a given electron anisotropy, because electrons themselves can be unstable to the electron whistler instability, which quickly lowers the anisotropy to levels where, in the absence of heavy ions, it is not sufficient to significantly change the balance between proton cyclotron and mirror mode. We agree that the electron whistler instability will not lead to complete isotropization of the electrons but only lower it to the instability threshold. In the parameter regime addressed, this limited isotropization will still eliminate the dominance of mirror mode and restore the usual dominance of the proton cyclotron mode, so our point still stands. Our simulations showed an isotropization of the electrons beyond the electron whistler threshold. In this reply, we will show that there are two contributing reasons: The nonlinear evolution of the mirror instability affects the electron anisotropy, as does unphysical numerical heating due to the limited resolution of a particle‐in‐cell simulation. We further discuss the coexistence of electron whistler instability and mirror instability, and we agree that both instabilities can be present in the magnetosheath.