A Three-Dimensional FDTD Magnetized Cold Plasma Model for Global Electromagnetic Wave Propagation.

摘要

For almost two decades, the finite-difference time-domain (FDTD) method has been applied towards modeling electromagnetic (EM) wave propagation within the Earth- ionosphere system. As computational resources continued to improve, global three-dimensional (3-D) FDTD models were developed and employed for studies of Schumann resonances, remote sensing of oil fields, remote sensing of ionospheric disturbances, and for modeling hypothesized electromagnetic earthquake precursors, etc.. All of the existing global FDTD models to date, however, have utilized an electrical conductivity profile to represent the ionosphere. As a result, the ionosphere is treated as a simple isotropic medium that ignores the influence of the geomagnetic field. This appears to be adequate in calculating the average propagation of EM waves below ∼100km altitude and at frequencies less than ∼1KHz over thousands of kilometers. However, by not including the anisotropic geomagnetic field, these global FDTD models are not capable of modeling many geomagnetism effects such as Faraday rotation in the ionosphere, whistler wave injection, and lightning-induced electron precipitation.;This dissertation aims to advance the global latitude-longitude FDTD model originally developed by Simpson and Taflove and having an isotropic ionosphere to an Earth-ionosphere model that accounts for the physics introduced by the magnetized ionospheric plasma. To generate this new global model, a 3-D Cartesian-coordinate magnetized cold plasma algorithm is first developed and rigorously validated. This algorithm has the capability to simulate wave behaviors in cold plasma under applied magnetic fields of arbitrary direction and magnitude. Plasma effects contributed by electrons, positive, and negative ions may all be included by this algorithm. A magnetic-field-independent absorbing boundary condition (ABC) is then proposed to truncate the computational domains that employ the cold plasma algorithm. Next, the Cartesian-coordinate magnetized cold plasma algorithm is fully adapted to Simpson and Taflove's latitude-longitude mesh to construct the new global ionospheric plasma FDTD model. This new simulator is believed to be the first. It will in particular permit higher frequency (above ∼1KHz) and higher altitude (above an altitude of ∼100km) propagation studies than permitted by all of the previous global models involving isotropic conductivity profiles.