Abstract
At equatorial and high latitudes, the intense ionospheric irregularities and plasma density gradients can seriously affect the performances of radio communication and satellite-based navigation systems; that represents a challenging topic for the scientific and engineering communities and operational use of communication and navigation services. The GNSS-based ROTI (rate of TEC index) is one of the most widely used indices to monitor the occurrence and intensity of ionospheric irregularities. In this paper, we examined the long-term performance of the ROTI in terms of finding the climatological characteristics of TEC fluctuations. We considered the different scale temporal signatures and checked the general sensitivity to the solar and geomagnetic activity. We retrieved and analyzed long-term time-series of ROTI values for two chains of GNSS stations located in European and North-American regions. This analysis covers three full years of the 24th solar cycle, which represent different levels of solar activity and include periods of intense geomagnetic storms. The ionospheric irregularities’ geographical distribution, as derived from ROTI, shows a reasonable consistency to be found within the poleward/equatorward boundaries of the auroral oval specified by empirical models. During magnetic midnight and quiet-time conditions, the equatorward boundary of the ROTI-derived ionospheric irregularity zone was observed at 65–70° of north magnetic latitude, while for local noon conditions this boundary was more poleward at 75–85 magnetic latitude. The ionospheric irregularities of low-to-moderate intensity were found to occur within the auroral oval at all levels of geomagnetic activity and seasons. At moderate and high levels of solar activity, the intensities of ionospheric irregularities are larger during local winter conditions than for the local summer and polar day conditions. We found that ROTI displays a selective latitudinal sensitivity to the auroral electrojet activity—the strongest dependence (correlation R > 0.6–0.8) was observed within a narrow latitudinal range of 55–70°N magnetic latitude, which corresponded to a band of the largest ROTI values within the auroral oval zone expanded equatorward during geomagnetic disturbances.
Highlights
Apart from its primary operational objective, the Global Navigation Satellite System (GNSS) has become one of the most important tools in ionospheric research
Time-series of GNSS rate of total electron content changes index (ROTI) values calculated for every station of the latitudinal chain are binned into small cells in magnetic latitude, and U.T.; a color of each cell represents an average intensity of ROTI
Previous studies of ROTI behavior at high latitudes [18,19] reported that ionospheric irregularity occurrence signatures, as derived from ground-based GNSS measurements, have a high degree of similarity with the auroral oval location and they can be discussed in terms of general auroral oval dynamics
Summary
Apart from its primary operational objective, the Global Navigation Satellite System (GNSS) has become one of the most important tools in ionospheric research. The greatest advantages over traditional techniques (such as radar/ionosonde and in situ plasma density measurements) are the global coverage and continuous, permanent availability [1,2,3,4]. Though GNSS signal frequencies have been chosen within the ionospheric disturbances resistant L–band, steeply and rapidly moving plasma density gradients may cause scintillations of the signals phase and intensity [5,6]. The problem of ionospheric plasma density irregularities is very complex, as it depends on a whole range of drivers—from the typical diurnal and seasonal ionization variation to the space weather induced events. Plasma density irregularities in auroral and subauroral latitudes are mainly caused by the auroral particle precipitation and high-speed plasma convection [7,8]. The scale of the processes—and the irregularities—can be substantially enlarged during geomagnetic storms and substorms [9,10]
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