Electrostatic ion-cyclotron waves driven by parallel velocity shear

Using a fluid treatment, it is shown that electrostatic waves with angular frequencies ∼ω ci (ion cyclotron frequency) propagating at large angles to the ambient magnetic field can be excited in a magnetized plasma by perpendicular shear in the magnetic field aligned plasma flow. The role of density gradients in determining the stability of shear-driven electrostatic ion-cyclotron (EIC) modes is also considered. These shear-driven modes may provide an explanation for observations of high frequency waves in the ionosphere.