| A study is presented in which the turbulent behavior of the daytime electrojet, the nighttime upper E region (120-140 km), and the nighttime bottomside F region (150-400 km) are examined near the magnetic equator. The resulting irregularities strongly affect satellite communications and cause radar system degradation. The analysis is based on a reformulation of the two-component fluid equations due to Barone resulting in a single equation. A quadratic approximation used therein results in a canonical equation which has previously served as the starting point for such well-known turbulence methods as the Direct Interaction Approximation (DIA) of Kraichnan.;In the first chapter, simulation of Type II irregularities of the daytime electrojet followed the interaction of a horizontal, linearly unstable irregularity wave and a vertical, linearly stable one. These simulations imitated other numerical investigations in examining this physical picture, suggested by Sudan, Akinrimisi, and Farley as the dominant small-scale generation mechanism there. However, unlike the turbulent behavior of investigations using the unapproximated fluid equations, the wave interaction evolved to highly regular behavior. This evolutionary outcome has also been seen in related simulations starting from quadratically nonlinear equations as demonstrated by Fornberg. Linear evolution of unstable waves seen in several simulations was investigated by a perturbation calculation, further corroborating the lack of the small scale generation mechanism in the computer runs. These and other findings support the conclusion that the quadratically approximated equations cannot duplicate the transition to turbulence seen in the unapproximated equations, through the above physical picture at least not for roughly comparable times or simulation parameters. However, the quadratically approximated equations appear to be well-suited for analysis of the steady state. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of school.) UMI. |
