Doppler clutter in HF radar systems produced by ULF waves

• Main Author: Sedeh, Leila Norouzi
• Other Authors: University of Newcastle. Faculty of Science & Information Technology, School of Mathematical and Physical Sciences
• Format: Thesis
• Language: English
• Published: 2014
• Subjects: ULF waves; HF signals; Seahr Alfven wave; wave propagation; FLR; plasmapause; ionosphere; superDARN; radar; Doppler clutter; Doppler velocity; Macquarie Island
• Online Access: http://hdl.handle.net/1959.13/1042283

Research Doctorate - Doctor of Philosophy (PhD) Ultra low frequency (ULF) waves are generated by the interaction of the solar wind with Earth’s magnetosphere. The waves propagate through the ionosphere and may be seen in data from SuperDARN Over-The-Horizon radars as oscillations in Doppler velocity which coincide with oscillations of the geomagnetic field recorded by ground magnetometers. Data from the two Tasman International Geospace Environment Radars (TIGER) and the magnetometer located on Macquarie Island over 2006-2009 show that ULF wave signatures are common. The dependence with time of day showed most ULF radar events occurred between 6-12 UT (dusk and pre-mid-night sector). Using the Maximum Entropy Method (MEM) several spectral aspects of detected ULF waves were investigated for the first time. Most of the recorded frequencies were in the range 1- 4 mHz. Some frequencies were seen more often than others with the more common frequencies spaced about 0.3mHz apart, consistent with previous studies. There was no evidence of a frequency dependence on latitude. Field line resonance (FLR) signatures in the radar data were expected but were not common, as shown by comparisons with coincident ground magnetometer data. This study has shown that most radar echoes containing ULF wave Doppler signatures appear to be backscattered from the plasmapause region mapped into the ionosphere. Modelling of the Doppler velocity combined with a ULF wave model and two dimensional ray tracing was achieved for the first time. The results are consistent with experimental observations. With further improvement, this modelling should provide a valuable tool to understand shear Alfven mode and fast mode plasma wave interactions within the ionosphere and their effects on HF propagation through the ionosphere.