| Summary: | Despite century-long efforts in assessing the electron density distribution in the Earth’s ionosphere and significant progress in identification of its major features, there are still many uncertainties with respect to the solar cycle’s seasonal and diurnal trends at various latitudes. Knowledge of these variations is needed for robust forecasting of the state of the ionosphere for the operation of practical radio systems, for example communication via high frequency radio waves. This thesis utilizes data from the incoherent scatter radar (ISR) at Poker Flat (Alaska, USA) to assess the diurnal and seasonal variations of three parameters of the ionospheric F2 region, the peak density, the height of the peak, and the thickness of the layer. These parameters are assessed for relatively high solar activity in 2014, and relatively low solar activity in 2016. Daytime electron densities were found to be largest during winter and spring and nighttime electron densities were found to be smallest in winter. Electron densities during the higher solar activity year were found to be greater than those during the lower solar activity year by a factor of 2-5, depending on the time of day, as expected. Details of the diurnal variations in electron density for various seasons are further discussed. ISR electron density data are also used for the validation of electron density measurements from Langmuir probes onboard the Swarm satellites in the topside ionosphere (~500 km). This work is an expansion of previous studies that use a different mode of ISR operation and a different approach to both ISR and Swarm satellite data handling. In addition to observations over Poker Flat (geographic latitude of ~60° N), observations over Resolute Bay, Canada at extreme high latitudes of ~80° are also considered. It is shown that, overall, the ratio of Swarm electron density measurements to those measured by ISRs is ~0.5-0.6 and that smaller ratios are observed at larger electron densities, usually during the daytime. At low electron ...
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