Drift-ion-sound standing waves are considered in a magnetized inhomogeneous plasma. Effects of three dimensionality, dispersion and vortex nonlinearity are taken into account. Perturbation theory solution is obtained by the multiple-time-scale formalism. It is shown that no secular terms are present up to the second order in amplitude and that second order corrections are homogeneous in the drift direction.
V. B. Taranov (Sat,) studied this question.