R. Chadwick

GPS phase scintillation and HF radar backscatter occurrence in the high-latitude ionosphere

The Canadian High Arctic Ionospheric Network (CHAIN) of ten dual-frequency GPS receivers has been operating since 2008. One-minute amplitude and phase scintillation indices and total electron content (TEC) are computed from data sampled at 50 Hz. The climatology of GPS phase scintillation for 2008-2009 [1] is updated to include year 2010 as the solar activity gradually increases and more coronal mass ejections impact the geospace. As a function of magnetic local time and geomagnetic latitude, the phase scintillation predominantly occurs in the cusp and the nightside auroral oval. The auroral phase scintillation shows an expected semiannual oscillation with equinoctial maxima known to be associated with aurorae, while the cusp scintillation is dominated by an annual cycle maximizing in autumn-winter. Depletions of the mean TEC are identified with the statistical high-latitude and mid-latitude troughs. Scintillation-causing irregularities may coexist with small-scale field-aligned irregularities detected as HF radar backscatter. The occurrence climatology of phase scintillation and of the HF backscatter at high latitudes are compared.

Experimental Evidence on the Dependence of the Standard GPS Phase Scintillation Index on the Ionospheric Plasma Drift Around Noon Sector of the Polar Ionosphere

First experimental proof of a clear and strong dependence of the standard phase scintillation index (σφ) derived using Global Positioning System measurements on the ionospheric plasma flow around the noon sector of polar ionosphere is presented. σφ shows a strong linear dependence on the plasma drift speed measured by the Super Dual Auroral Radar Network radars, whereas the amplitude scintillation index (S4) does not. This observed dependence can be explained as a consequence of Fresnel frequency dependence of the relative drift and the used constant cutoff frequency (0.1 Hz) to detrend the data for obtaining standard σφ. The lack of dependence of S4 on the drift speed possibly eliminates the plasma instability mechanism(s) involved as a cause of the dependence. These observations further confirm that the standard phase scintillation index is much more sensitive to plasma flow; therefore, utmost care must be taken when identifying phase scintillation (diffractive phase variations) from refractive (deterministic) phase variations, especially in the polar region where the ionospheric plasma drift is much larger than in equatorial and midlatitude regions.

High-latitude GPS TEC changes associated with sudden magnetospheric compression

The Earths ionosphere is embedded in the “magnetosphere” a cavity carved by the interaction of the high-speed solar wind and its “frozen-in” magnetic field with the terrestrial magnetic field. The solar wind is inherently non-steady, with its magnetic field, density, and flow speed varying on a range of time and amplitude scales. Variations in the solar wind and its magnetic field are known to be the major driver of variations in the high-latitude ionosphere. Using ionospheric total electron content (TEC) measured by Global Positioning System (GPS) receivers of the Canadian High Arctic Network (CHAIN), we provide clear evidence for a systematic and propagating TEC enhancement produced by the compression of the magnetosphere due to a sudden increase in the solar wind dynamic pressure. The magnetospheric compression is evident in the THEMIS/GOES data. Application of a GPS triangulation technique revealed that the TEC chnages propagated with a speed of ∼ 6 km/s in the antisunward direction near noon and ∼ 7 km/s in the sunward direction in the pre-noon sector. This is consistent with the scenario of increased ionospheric convection due to the magnetospheric compression. The characteristics of the TEC changes seems to indicate that they are due to the particle precipitation associated with the sudden magnetospheric compression.