Nonlinear two-stream instabilities as an explanation for auroral bipolar wave structures



The evolution of two counter-streaming electron beams is shown by means of 2-D kinetic simulations to lead to electron distributions and coherent localized bipolar plasma wave structures with features similar to those measured by the FAST satellite in the auroral ionosphere. Electrostatic whistler waves are generated at later times when the bipolar structures begin to lose coherence and break up in the dimension transverse to the geomagnetic field.