Theoretical Study of Ground-Based Auroral Radio Emissions

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The objective of the project is to address several key theoretical issues relevant to the frequency-range from 5kHz to 5MHz radio waves observed on the ground in the auroral zone, known as auroral roars. With the previous support from NSF, the PI and his colleagues were able to provide basic explanations for two types of emissions - the continuum roars are generated within the density depletion near the F -region source, while the discrete roars are eigenmodes of density enhancements. A key ingredient common to both types of emissions are the generation of upper-hybrid, or Z -mode waves, and their conversion to electromagnetic waves. The previous research project was largely concerned with the characterization and understanding of the generation process of upper-hybrid/Z -mode waves. The focus of the proposed research will be on the conversion and/or coupling of Z -mode waves to electromagnetic waves. Such a study is essential to put the theories of continuum and discrete roar emissions on a fully viable footing.