Plasma irregularity production in the polar cap f-region ionosphere

• Main Author: Lamarche, Leslie
• Other Authors: Makarevich, Roman, Bristow, William, Conde, Mark, Zhang, Hui
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 2017
• Subjects: Fairbanks; Antarc*; Antarctica; Alaska
• Online Access: http://hdl.handle.net/11122/7619

Dissertation (Ph.D.) University of Alaska Fairbanks, 2017 Plasma in the Earth's ionosphere is highly irregular on scales ranging between a few centimeters and hundreds of kilometers. Small-scale irregularities or plasma waves can scatter radio waves resulting in a loss of signal for navigation and communication networks. The polar region is particularly susceptible to strong disturbances due to its direct connection with the Sun's magnetic field and energetic particles. In this thesis, factors that contribute to the production of decameter-scale plasma irregularities in the polar F region ionosphere are investigated. Both global and local control of irregularity production are studied, i.e. we consider global solar control through solar illumination and solar wind as well as much more local control by plasma density gradients and convection electric field. In the first experimental study, solar control of irregularity production is investigated using the Super Dual Auroral Radar Network (SuperDARN) radar at McMurdo, Antarctica. The occurrence trends for irregularities are analyzed statistically and a model is developed that describes the location of radar echoes within the radar's field-of-view. The trends are explained through variations in background plasma density with solar illumination affecting radar beam propagation. However, it is found that the irregularity occurrence during the night is higher than expected from ray tracing simulations based on a standard ionospheric density model. The high occurrence at night implies an additional source of plasma density and it is proposed that large-scale density enhancements called polar patches may be the source of this density. Additionally, occurrence maximizes around the terminator due to different competing irregularity production processes that favor a more or less sunlit ionosphere. The second study is concerned with modeling irregularity characterics near a largescale density gradient reversal, such as those expected near polar patches, with a particular ...