Ground-based interferometric studies of auroral roar

Auroral roar is a naturally-occurring radio emission generated in the Earth's auroral ionosphere at frequencies near 3 MHz and 4.5 MHz and believed to occur at harmonics of the ionsopheric electron cyclotron frequency (2 fce and 3fce). Although the first observations of auroral roar were reported more than 20 years ago, a satisfactory mechanism for generating the emissions has not been found. A principle reason for this is that previous studies have been made using non-directional antennas which give no information about the location of the auroral roar source regions.; This thesis describes the development of the medium-frequency interferometer (MFI), the first direction-sensitive instrument capable of detecting auroral roar events, and discusses a series of experiments designed to study the generation mechanism and propagation characteristics of 2fce auroral roar. Data from the MFI reveal that auroral roar is generated in both the bottom and top sides of the ionsopheric F-region and that it can propagate to the ground from both these locations. The data also reveal that individual auroral roar events often propagate to the MFI from more than one direction, implying the existence of more than one source region. Statistical and case study analyses suggest that auroral roar is usually generated near the poleward edge of the auroral oval.; Electron density measurements from the Sondrestrom incoherent scatter radar have been used to test one candidate generation mechanism which suggests that 2fce auroral roar is generated as an electrostatic upper hybrid wave at places where the upper hybrid frequency matches twice the electron cyclotron frequency. In each of the five available cases, this matching condition is met in the auroral roar source region. Finally, observations and numerical simulations of a recently observed phenomenon known as flickering auroral roar are presented. Numerical simulations suggest that flickering auroral roar may be caused by auroral particle flux modulations caused by, the presence of electromagnetic ion cyclotron waves.