Ionospheric TEC Gradient Magnitude Distribution over the Brazilian Airspace

Using a chain of ground-based GPS receiver stations from the Brazilian RBMC network, we studied the distribution of ionospheric total electron content (TEC) gradient magnitudes over the Brazilian airspace and its variation throughout the maximum phase of Solar Cycle 24. The GPS receiver stations form an east-west chain along the southern crest of the equatorial ionization anomaly, where the largest TEC gradient magnitudes and the most severe cases of ionospheric scintillation are expected to occur due to equatorial plasma bubbles. The focus of this effort was to define the systematic variation of nighttime TEC gradient magnitude distribution in the region over several years 2011-2016 during Solar Cycle 24. We found that the nighttime ionospheric TEC gradient magnitude distribution in each year follows a form of double-power-law distribution with a clearly visible break, in general agreement with a number of previously reported results [Pradipta and Doherty, 2016a, 2016b; Pradipta et al., 2016]. Furthermore, we also found that the two exponents of the aforementioned double-power-law vary systematically from one year to the next following the progression of the solar cycle. In the year(s) when the sunspot number was higher, the tail of the TEC gradient magnitude distribution shifted upward, indicating a more frequent occurrence of extreme TEC gradients over the area. Numerical extrapolation into future solar cycles would be possible based on the best fit lines that we have derived for the double-power-law exponents as a function of the international sunspot number. It is hoped that the these findings would be useful for projecting the level of threats to GBAS/SBAS operation at low-latitude regions during various phases of the solar cycle, and hence help establish a firm/stable route for implementing GBAS/SBAS services around the globe.