Morphological Features of Ionospheric Scintillations During High Solar Activity Using GPS Observations Over the South American Sector

摘要

The main objective of this study is to investigate the ionospheric irregularities observed by Global Positioning System-total electron content (GPS-TEC) receivers during the high solar activity years of 2013 and 2014 at different stations in the equatorial and low-latitude regions in the South American sector. The ionospheric parameters used in this investigation are the TEC, the rate of change of the TEC index (ROTI), and the amplitude scintillation index (S4). In the South American sector, the ROTI and S4 indices showed that the ionospheric irregularities have an annual variation with maximum occurrence from September to April, between 20:00 LT and 02:00 LT, and no occurrence from May to August. Also, strong phase fluctuations (ROTI >1) are observed over South America at 19 LT in October and November. Morlet wavelet analysis of ROTI and S4 showed that planetary wave-scale periods ranging from 2 to 8 days are predominant during September-March at 20-02 LT in South America. In addition, using a keogram it was possible to evaluate the distance between adjacent ionospheric plasma depletions, and this result is presented and discussed. The longitudinal distances between adjacent bubbles vary around ~600-1000 km, which is larger than values reported in most previous studies.