Investigation of Scintillation Characteristics for High Latitude Phenomena

High latitude irregularities in electron density have dimensions of meters to kilometers and can cause severe scintillation effects for GNSS signals traveling through this region of the ionosphere. Extreme scintillation effects, and associated degradation or loss of navigation capabilities, have been observed in North America for severe events. Auroral scintillation has been studied for decades, with typically strong phase scintillation and weak amplitude scintillation observed at high latitudes due to the precipitating electrons. Auroral scintillation is most commonly observed at nightside local times. Since 2003 the University of Calgary has operated a number of specialized GPS receivers in Canada for ionosphere monitoring - as part of the CANGIM (CANadian GPS Network for Ionosphere Monitoring). These receivers are modified dual-frequency survey-grade NovAtel Euro4 receivers, with specialized firmware capable of deriving phase and amplitude scintillation information. These data have been collected at three sites in western Canada over the past five years. These sites are located at similar longitudes and over a range of latitudes spanning the sub-auroral region into the polar cap. Observations from the three stations allow latitude profiling of the spatial extent of scintillation effects. In this paper, we investigate nightside auroral scintillation using the extensive CANGIM GPS data set. Scintillation events throughout the years 2003-2007 are identified. In order to better understand the nature of these effects, the CANGIM data are also augmented with observations from spaceborne GPS receivers. GPS observations from the CHAMP satellite are used to infer the presence of ionospheric irregularities at various altitudes. For an occulting GPS satellite, the line-of-sight to the low-Earth orbiter (LEO) successively passes though horizontal layers at different altitudes. Times series of such observations can therefore reflect the presence of smallscale electron density variations in a given height range if rapid random phase variations are observed. When considered in conjunction with the ground-based scintillation measurements in Canada, local LEO observations are therefore used to determine the vertical extent of irregularities. The nature of physical processes leading to formation of these irregularities (and associated scintillation effects) is then determined. Results are applicable to the development of physics-based scintillation simulations - which are used to assess GNSS receiver tracking performance.

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