Falling-tone chorus: theory and simulations

During the last few years, improved observations indicate that falling-tone chorus (fallers) has characteristics that are quite different from rising-tones (risers). Among the most important characteristics that distinguish fallers from risers are: large angles of propagation and usually lower maximum amplitudes. These characteristics make fallers more difficult to simulate numerically than risers. Recently, we have developed a new model that successfully accounts for fallers. The model proposes that fallers start as a marginally unstable mode, which requires a balance between growth and damping, attributable to the Landau damping of oblique waves in this collisionless environment. The extension of the theory to risers will be discussed.