Title page for ETD etd-03142009-040454
|Type of Document
||Fourier spectral methods for numerical modeling of ionospheric processes
||Master of Science
|Scales, Wayne A.
|Besieris, Ioannis M.
|Claus, Richard O.
|Date of Defense
Fourier spectral and pseudospectral methods are used in numerical modeling of ionospheric
processes, namely macroscopic evolution of naturally and artificially created ionospheric
density irregularities. The simulation model consists of two-dimensional electrostatic
nonlinear fluid plasma equations that describe the plasma evolution. The spectral
and pseudospectral methods are used to solve the spatial dependence of these self-consistent
equations. They are chosen over the widely used finite difference and finite element techniques
since spectral methods are straightforward to implement on nonlinear equations.
They are at least as accurate as finite difference simulations. A potential equation solver is
developed to solve the nonlinear potential equation iteratively. Time integration is accomplished
using a combination of leapfrog and leapfrog-trapezoidal methods. A FORTRAN
program is developed to implement the simulation model. All calculations are performed
in the Fourier domain.
The simulation model is tested by considering three types of problems. This is accomplished
by specifying an initial density (Pedersen conductivity) profile that represents slab
model density, density enhancement (due to releases such as barium), or density depletion
(due to late times effects of electron attachment material releases) in the presence of a neutral
wind. The evolution of the irregularities is monitored and discussed. The simulation
results agree with similar results obtained using finite difference methods. A comparison
is made between the ionospheric depletion and enhancement problems. Our results show
that, given the same parameters and perturbation level, the depletion profiles bifurcate
much faster than that of the enhancement. We argue that this is due to the larger growth
rate in the E X B interchange instability of the density depletion case.
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