VHF radar aurora : statistics, fading and correlation with optical aurora

Abstract

This thesis presents the studies of aurora using three observation instruments; the SAPPHIRE SOUTH VHF radar system, the ASC (All-Sky Camera) system at Rabbit Lake, Saskatchewan, and the 50-MHz CW (Continuous Wave) bistatic Doppler radars in the 1981 campaign. The SAPPHIRE SOUTH radar system, which has a high temporal and frequency resolution, is a multi-beam CW bistatic VHF Doppler radar system. Two transmitters, located at La Crete (Alberta), and Gillam (Manitoba), transmitted on four transmitter beams for each transmitter and intersected with four receiver beams from Saskatoon, Saskatchewan to form 32 radar target regions in the lower E-region of the ionosphere. The ASC system at Rabbit Lake provides digitized high resolution optical auroral images at several wavelengths (557.7 nm, 630.0 nm) and for the whole visible spectrum. The observing region of the ASC system covered all the radar target regions of the SAPPHIRE SOUTH radar system. The 50 MHz CW bistatic Doppler radars in the 1981 campaign had a special radar setup with three transmitters and two receivers to provide multiple radar beams with different aspect and flow angles. The AE index and Kp index data have been compared with the radar Doppler spectral characteristics extracted by using software designed for peak-finding and curve-fitting. The radar data received by the SAPPHIRE SOUTH radar system have been compared with the optical data obtained by the ASC: system in Rabbit Lake. The results showed that strong Type 1 and Type 3 radar auroral echoes were received along the auroral arc alignment while weak Type 2 echoes were observed in the direction perpendicular to the auroral arc alignment. The power of radar auroral echoes received along the auroral arc alignment was well correlated with the standard deviation of the optical auroral emission inside the radar target region. The non-linear theory of the Type 3 radar auroral echoes has also been examined. A fading analysis has been applied to the SAPPHIRE SOUTH radar data to examine whether the electromagnetic ion cyclotron (EMIC) wave caused the fading of VHF radar auroral signals. The results showed that fading frequency ranges of Type 3 and Type 4 echoes were consistent with electric field oscillation and primary particle modulation arising from EMIC waves. The results of statistical studies on the data obtained from the radars in the 1981 campaign showed that the power of radar auroral backscatter echoes received by the radar link with a large aspect angle (4.08°) and a small assumed flow angle (6.17°) correlated well with the AE index. Regardless of the AE index, strong radar auroral backscatter echoes were observed by the radar link with smallest aspect angle (1.57°). Type 1 and Type 5 radar auroral backscatter mostly occurred for large values of the AE index, while Type 2 and Type 3 radar auroral backscatter echoes were mostly observed for small values of the AE index.