RESEARCH ON SPREAD-F STUDIES.
AVCO CORP WILMINGTON MASS RESEARCH AND ADVANCED DEVELOPMENT DIV
Pagination or Media Count:
The results of ionospheric observations using a variety of techniques are summarized to show that magnetic-fieldaligned irregularities exist in the ionosphere. A critique of theories explaining why the irregularities cause spread echoes is given. Statistical studies of the geographic and temporal variations in spread-F occurrence are summarized. The fundamental question of how irregularities causing spread F are produced in the ionosphere is discussed. It is suggested that incoming charged particles traveling down magnetic-field lines to F-region heights create field-aligned ionization which is masked during the day by photoionization. The proposed mechanism is supported by observational results in polar regions. A theoretical treatment of the formation of the ionosphere over the pole at winter solstice indicates that photoionization alone is inadequate to explain observed electron densities in the F layer, and an additional production mechanism such as incoming charged particles is needed. A study of traveling disturbances at high latitudes reveals that the phenomenon is invariably followed by spread-F conditions. An analysis of WWV reception at high latitude is discussed to show the effects of spread F on high-frequency HF communications circuits. Author