Counter-rotating coupled drift-acoustic vortices in the presence of sheared ion flows

Nonlinear equations governing the dynamics of finite amplitude drift-acoustic-waves are derived, taking into account sheared ion flows. A new class of stationary solution of the nonlinear equations can be represented in the form of a counter-rotating vortex. The latter appears in those parameter regimes in which the formation of a dipolar vortex is forbidden. For a large perpendicular ion velocity shear parameter, a counter-rotating vortex is similar to a vortex chain. The newly found counter-rotating vortex can be correlated with coherent nonlinear structures that are observed in association with sheared plasma flows in space and laboratory environments.