Saturation of the Farley-Buneman instability via three-mode coupling

摘要

Characteristics of type-1 radar echoes obtained from the E region ionosphere have yet to be conclusively explained. The dynamical properties of the saturated state of the Farley-Buneman instability are widely thought responsible for these type-1 echoes. In this paper we present a different perspective and new details on a previously proposed three-wave coupling mechanism (Otani and Oppenheim, 1998) for the saturation of the Farley-Buneman instability. A novel method is presented for the analysis of general, three-wave systems with stationary, sinusoidal solutions. Computer simulations of the three-wave system produce steady states in close agreement with those obtained from the method. Despite the fact that the system only contains three modes, a number of features also agree well with observation, including density fluctuation magnitudes (∣δn∣/n 0 = 5%), propagation speeds (clustered around the sound speed), and power falloff as a function of elevation angle. We demonstrate how the spatial distributions of the phases of the electron advection term and electron E × B velocity for the secondary modes lead to the partial cancellation of the destabilizing zero-order electron drift, thereby saturating the Farley-Buneman instability. The mechanism is consistent with the one previously advanced, which described saturation of the instability in terms of the diversion of electron flow around density peaks.