- Direct analysis of mirror mode instabilities from the general dielectric tensor for several model distributions in the long wavelength limit is performed. The growth rate at the instability threshold depends on the derivative of the distribution for zero parallel energy. The maximum growth rate is ∼ k∥vT∥ well above the instability threshold. The instability threshold and growth rate and their dependence on the propagation angle depend on the shapes of the ion and electron distribution functions. © 2001 American Institute of Physics.