Abstract
GPS measurements obtained by the global IGS network were used to study the occurrence of TEC fluctuations in the northern and southern high-latitude ionosphere during severe geomagnetic storms. In the northern hemisphere, GPS stations located higher than 55N Corrected Geomagnetic Latitude (CGL) at different longitudes were selected. In the southern hemisphere, Antarctic permanent GPS stations were used. Dual-frequency GPS measurements for individual satellite passes served as raw data. As a measure of fluctuation activity the rate of TEC (ROT) was used, and the fluctuation intensity was evaluated using the ROTI index. Using daily GPS measurements from all selected stations, images of the spatial and temporal behavior of TEC fluctuations were formed (in Corrected Geomagnetic Coordinates—CGC and geomagnetic local time—GLT). Similarly to the auroral oval, these images demonstrate an irregularity oval. The occurrence of the irregularity oval relates to the auroral oval, cusp and polar cap. During a storm, the intensity of TEC fluctuations essentially increased. The irregularity oval expands equatorward with an increase of magnetic activity. The study showed that the existing high-latitude GPS stations can provide a permanent monitoring tool for the irregularity oval in near real-time. In this paper, the features of the development of phase fluctuations at the geomagnetic conjugate points, and inter-hemispheric differences and similarities during winter and summer conditions, are discussed.
Highlights
It is known that GPS radio signals passing through the ionosphere suffer varying degrees of rapid variations of their amplitude and phase—signal scintillations
The comprehensive image of TEC fluctuations and ionospheric irregularities was obtained using multi-station GPS measurements collected at stations located higher than 50◦ Corrected Geomagnetic Latitudes (CGL) that monitor the polar, auroral and subauroral ionosphere
To the results presented above, the spatial and temporal occurrence of the irregularities can be graphically presented in magnetic local time (MLT) and Corrected geomagnetic latitude (CGL) coordinate system
Summary
It is known that GPS radio signals passing through the ionosphere suffer varying degrees of rapid variations of their amplitude and phase—signal scintillations. Phase scintillations at frequencies much lower than the Fresnel frequency are caused by irregularities with scale sizes that are much larger than the size of the first Fresnel zone Under such conditions, refraction effects can be taken into account and the phase fluctuations are due to the optical path changes of a radio wave (Pi et al, 1997). In a previous study, Shagimuratov et al (2009) reported differences in the occurrence of GPS phase fluctuations during a geomagnetic storm in the Northern and Southern hemispheres. GPS measurements of the selected stations have enabled a study of the differences, and similarities, of the occurrence of TEC fluctuations over the Northern and Southern hemispheres. The comprehensive image of TEC fluctuations and ionospheric irregularities was obtained using multi-station GPS measurements collected at stations located higher than 50◦ Corrected Geomagnetic Latitudes (CGL) that monitor the polar, auroral and subauroral ionosphere
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