Incoherent Scatter Spectral Theories—Part II: Modeling the Spectrum for Modes Propagating Perpendicular to B

Abstract

Incoherent scatter (IS) spectral models for collisional and magnetized F-region plasmas are developed based on a general framework described in part I of this paper and on the statistics of simulated particle trajectories. In the simulations, a Langevin update equation is used to describe the motion of charge carriers undergoing Coulomb collisions. It is shown that random displacements of oxygen ions in the F-region can be characterized as a Brownian-motion process with Gaussian distributed displacement vectors. Electron displacements, on the other hand, are non-Brownian, and their statistics exhibit a dependence on the magnetic aspect angle. A numerical library of characteristic functions of electron displacements was constructed from the simulation data obtained for a set of plasma parameters typical of the equatorial F-region. Spectral models for the IS radar signals from F-region heights are constructed with one-sided Fourier transforms of the characteristic functions of electron and ion displacements. The models are valid at all magnetic aspect angles, including the zero aspect angle that corresponds to radar observations perpendicular to the ambient geomagnetic field B.