EXCITATION OF GEOMAGNETIC MICROPULSATIONS BY MEANS OF IONOSPHERIC CONDUCTIVITY CHANGES INDUCED BY SOLAR FLARES. (VOLUMES I AND II) (HYDROMAGNETIC, MODE CONVERSION, WAVE POLARIZATION)

In this thesis we develop the premise that solar flares with large components in the X-ray and EUV spectra stimulate geomagnetic pulsations in the earth's magnetosphere by means of sudden conductivity changes in the dayside ionosphere. Ground-based observations of 7-22 mHz (Pc4 band) magnetic pulsations are shown to be associated with conductivity enhancements for four selected solar flare events in 1980. Magnetic activity was measured at four stations in a meridional chain in the U.S. and Canada having magnetic shell parameters (L-values) between 3.2 and 4.4 and a conjugate station in Siple, Antarctica. Solar X-ray flux data from earth-orbiting satellites are used with an energy deposition model to calculate the time-dependent height-integrated conductivity tensor in the ionospheric region above each magnetometer site. Hydromagnetic wave theory is initially applied to a simple model of a cold magnetospheric plasma and a plane, anisotropic, conducting ionosphere to determine reflection coefficients and induced currents in the presence of reflected wave mode conversion. The model is expanded to include a dipole field and a "zero-phase approximation" of the hydromagnetic wave equation is integrated to obtain predicted eigenperiods. It is found that these eigenperiods closely match the observed excited wave periods for reasonable equatorial plasma densities. Finally, a procedure is developed for interpreting wave polarization data at ground magnetometer sites. The treatment of reflected wave mode conversion, the use and application of the zero-phase approximation, and the interpretation of wave polarization are believed to be new developments.