Long-term Variations in HF radar Backscatter

This thesis studies the long term variation of the high latitude ionosphere and its activity. A statistical analysis of backscatter data spanning 20 years from 1996 to 2015 in the total field of view of the two HF radars was carried out in order to determine the solar cycle, the annual and the diurnal variations of backscatter (ionospheric scatter and ground scatter) in both Super Dual Auroral Radar Network (SuperDARN) radars over a longer time period. Increase in ionospheric scatter during solar maximum previously anticipated by Milan et al., (1997b) and higher occurrence of ground scatter than ionospheric scatter were observed in the analysis. The study in this thesis also includes investigation on the propagation mode responsible for the occurrence of ionospheric and ground backscatter. Similar to the data used in the first analysis, 20 years of data from three selected beams were employed. In this study, it was found that occurrence of ionospheric backscatter is prominent at far ranges at local day during solar cycle 23 than solar cycle 24. The analysis shows that occurrence of ionospheric scatter is seen at mid-range gates during summer in contrast to similar study carried out by Milan et al.(1997b) which identifies near range gates ionospheric scatter during similar period. In addition, a study to identify the parameter or parameters that can be used for adequate prediction and forecast of occurrence of ionospheric backscatter for both short and long term durations was carried out. The percentage occurrence of ionospheric scatter as a function of the selected parameters in spring, summer, autumn and winter from January 1996 to January 2016 in the four magnetic local times were analysed. The study increases our understanding on the global factors responsible for the occurrence of ionospheric scatter and the local time variation on the occurrence rate. It also raises some interesting questions.