Ion Bernstein waves driven by two transverse flow layers

The interaction between two narrow layers of E×B flow is investigated, along with their stability properties. The mode frequencies, growth rates, and eigenfunctions are calculated. It is found that the instability due to a single layer is robust to the inclusion of a second layer. Specifically, when the separation between the layers is on the order of the ion-cyclotron radius, there is strong coupling between the two layers and the second layer is destabilizing. In addition, when the flow velocities are in opposite directions a wide variety of modes is possible, including near-zero-frequency modes, resulting in broadband structure in both the frequency spectrum and the wave number spectrum. These results may have implications for the understanding of the auroral ionosphere, where such spatial structure in the transverse electric field is often observed.