Sources and Causes of Upper Atmospheric Disturbances

摘要

In the past three years we conducted theoretical and experimental studies of somenaturally occurring ionospheric disturbances. Periodic amplitude variations of satellite beacon signals were observed as the precursors of the plumes of equatorial ionospheric irregularities. Some outstanding features of explosive spread F reported in Woodman and La Hoz and Woodman and Kudeki can be reasonably understood in terms of the lightning induced electromagnetic effects. The spectral broadening of monochromatic VLF radio signals detected by satellites in the topside ionospheric was attributed to the nonlinear scattering of waves off ionospheric density irregularities. Furthermore, the irregularity anisotropy can give rise to prominent effects on the Faraday polarization fluctuations of linearly polarized radio signals. This fact can be used to develop the radio diagnostics of the anisotropic nature of ionospheric irregularities, namely, to determine the geometry of field-aligned density irregularities. Efforts were also made on the reduction of ionospheric effects on the polarization measurements during satellite tracking.