The instability of the electromagnetic ordinary modes in counterstreaming and counterrotating plasmas

The instability of a linearly-polarised electromagnetic ordinary mode in counterrotating plasmas and propagating perpendicular to a uniform magnetic field caused by a counterstreaming of electrons along the latter is studied using a cold-plasma model. It is found that: (i) In the presence of either a streaming or a rotation or both, the ordinary-wave propagation is possible even for frequencies less than the plasma frequency; (ii) the Coriolis forces like the applied magnetic field stabilise the ordinary modes.