Modeling of the polar ionosphere in the inertial corotating frame

Abstract

The ionospheric model presented in this thesis is developed from first principles. It is a three-dimensional and time-dependent model that covers the region poleward from 50 degrees of geographic latitude and extends to the height range of 80-500 km. In this model, equations of continuity, motion, and energy balance are self-consistently solved for the densities of 7 ion species $\lbrack O\sp+(\sp4S,\ \sp2D,\ \sp2P),\ NO\sp+,\ O\sb2\sp+,\ N\sb2\sp+,\ N\sp+\rbrack$ and electrons. The model accounts for 40 photochemical processes, the neutral wind drag with its shear, electromagnetic E $\times$ B-drift, and field-aligned ambipolar diffusion. The background thermospheric parameters here are derived from the VSH/MSIS models. Minor species $NO,\ N(\sp4S,\ \sp2D)$ and their molecular and eddy diffusion transfer in the lower ionosphere are considered in this model. Energy balance equations for isotropic electron and ion temperatures are solved. including electron thermal conduction and Joule heating. The model is applicable to a limited polar region (hence the curvature is neglected) and the equations are solved in the corotating Cartesian frame with an azimuthal equidistant projection of all parameters and point-by-point transformation of the inputs specified in the geomagnetic frame. The regular grid has a scaleable resolution; the workstation version of the code presented in this thesis has achieved 100 x 100 km horizontal resolution. The algorithm maintains numerical stability for variable time steps in the range from 10-15 minutes to 1-2 minutes, allowing a flexible time coverage. This effective algorithm and even spatial coverage of the regular grid saves significant computational resources. The model output realistically represents seasonal changes and other large-scale polar ionospheric features such as the abundant day-side ionization, the polar cap tongue of ionization, the auroral oval, the polar hole, and ionospheric troughs of different origins. Ionospheric simulations developed in response to different IMF variations demonstrate destruction of continuous polar cap structures and the creation of "patches" of ionized plasma. Several model simulations have shown good overall agreement with observed ionospheric events.