Characteristics of Low Midlatitude GPS Ionospheric Scintillations over Australia and Niue

Scintillations of electromagnetic waves passing through the Earth's ionosphere are induced by electron density irregularities, which could result in loss of lock for the signals of GNSS (Global Navigation Satellite System). In this paper, the characteristics of the southern hemisphere low midlatitude GPS ionospheric scintillations were investigated utilizing GPS amplitude scintillations data recorded by GPS receivers installed at Darwin (12.45°S, 130.95°E; magnetic latitude: 21.96°S) and Weipa (12.63°S, 141.88°E; magnetic latitude: 21.79°S) of Australia and Niue (19.07°S, 190.07°E; magnetic latitude: 20.84°S), respectively. The data set recorded between January 2013 and December 2016 was analyzed, including the peak year of the solar activity cycle 24 (i.e., 2014). The results indicate that scintillation at the three stations took place mostly at night. For the three stations, the annual scintillation occurrence rate enhanced with the enhanced solar activities from 2013 to 2014, and decreased with the decreased solar activities from 2015 to 2016. For all of the three stations, the annual scintillation occurrence rate was largest and the scintillation duration was longest in 2014. The features of scintillations over Darwin and Weipa were similar, namely, scintillation occurred mainly in the equinoctial months. In addition, the scintillation occurrence at Darwin and Weipa presented significant equinoctial asymmetry, especially in 2014. That is to say, scintillation took place more frequently in autumn (i.e., March-April) than in spring (i.e., September-October) over Darwin and Weipa. However, scintillations over Niue occurred mainly during the equinoctial months and July-August (i.e., winter), especially in 2014. S 4 recorded at Darwin, Weipa, and Niue often exceeded 0.6 between 2013 and 2015, which shows that the negative impacts of ionospheric scintillation are very severe even for low midlatitude (~21° magnetic latitude) GNSS receivers during the high solar activity period.