A measurement of small-scale features using ionospheric scintillation. Comparison with refractive shift measurements

Abstract

We present a study of scintillation induced by the mid-latitude ionosphere. By implementing methods currently used in Interplanetary Scintillation studies to measure amplitude scintillation at low frequencies, we have proven it is possible to use the Murchison Widefield Array to study ionospheric scintillation in the weak regime, which is sensitive to structures on scales $\sim$300 m at our observing frequency of 154 MHz, where the phase variance on this scale was 0.06 rad${}^2$ in the most extreme case observed. Analysing over 1000 individual 2-minute observations, we compared the ionospheric phase variance with that inferred with previous measurements of refractive shifts, which are most sensitive to scales almost an order of magnitude larger. The two measurements were found to be highly correlated (Pearson correlation coefficient 0.71). We observed that for an active ionosphere, the relationship between these two metrics is in line with what would be expected if the ionosphere's structure is described by Kolmogorov turbulence between the relevant scales of 300m and 2000m. In the most extreme ionospheric conditions, the refractive shifts were sometimes found to underestimate the small-scale variance by a factor of four or more, and it is these ionospheric conditions that could have significant effects on radio astronomy observations.

12 pages, 9 figures, 1 table, accepted for publication in PASA

References in corpus (5)

• Characterisation of the ionosphere above the Murchison Radio Observatory using the Murchison Widefield Array
• Interplanetary Scintillation studies with the Murchison Wide-field Array II: Properties of sub-arcsecond compact sources at low radio frequencies
• Emergence and disappearance of micro-arcsecond structure in the scintillating quasar J1819+3845
• A Measurement of Source Noise at Low Frequency: Implications for Modern Interferometers
• Sub-kilometre scale ionospheric studies at the SKA-Low site, using MWA extended baselines

Cited by in corpus (2)

• Detection and Characterisation of a Coronal Mass Ejection using Interplanetary Scintillation measurements from the Murchison Widefield Array
• Ionospheric contributions to the excess power in high-redshift 21-cm power-spectrum observations with LOFAR