Ionospheric Phenomena and Low-Frequency Radio Astronomy

The Murchison Widefield Array radio telescope (MWA), situated on the Murchison Radio Observatory (MRO) in Western Australia, has recently commenced operations. This instrument operates over the frequency range 80-300 MHz. Further, the MRO is also the site chosen to host the low-frequency component of the Square Kilometre Array, radio telescope (SKA). Each instrument is susceptible to scintillation caused by fluctuations in ionospheric plasma density and Faraday rotation of incoming signals caused by the interaction of low-frequency radio waves with dissociated electrons in the ionosphere. Observations of these parameters over several years, across periods of both subdued and elevated solar activity have demonstrated markedly differing regimes. High-precision GPS systems, combined with purpose-written data acquisition software (SCINDA), have enabled investigation of various phenomena including the effect of solar storms on the ionosphere at highly resolved time-scales. We report on aspects of phenomena observed and their significance to low-frequency radio astronomy and note that conditions of very low scintillation encountered support the decision to site world-leading instruments on the MRO.