Statistical Analysis of TEC Distributions Observed Over South and Central America

Abstract

AbstractTotal electron content (TEC) values measured with several arrays of dual‐frequency GPS receivers operating continuously and simultaneously at equatorial and low latitudes are used to construct regional maps of TEC over South and Central America and the Caribbean region. This extended database comprises TEC values collected by 126 stations that operated in South America in 2008, 181 stations in 2009, and 324 stations in 2010. The latter year includes GPS stations in Central America and the Caribbean region, extending the TEC coverage from the southern tip of South America to the northern boundary of Mexico (~30°N latitude). The TEC maps contain high (0.5° × 0.5°) spatial resolution and good (30 min) temporal resolution. The most prominent feature of these maps is the day‐to‐day variability that is observed during all seasons and under quiet and active magnetic conditions. Single station plots display TEC variations with time scales of few hours and the appearance of TEC enhancements near‐midnight that can be accounted for by electric fields associated with disturbed magnetic conditions and the reverse fountain effect, respectively. To assess the TEC dependencies upon season, solar flux, magnetic activity, and local time over South and Central America, two statistical procedures were employed. First, we constructed monthly averages of TEC values along three field lines that intersect the magnetic equator at 70°, 60°, and 50°W longitudes that show a complex pattern of variability and symmetry/asymmetry of the equatorial anomaly depending on the season, the longitude, and the solar flux. Our second analysis consists of a non‐linear least‐square fit to simultaneously extract the solar flux, magnetic, and seasonal dependencies of TEC for each square cell (0.5° × 0.5°) of the regional maps and for each 30‐min time sector. It is found that during low solar flux conditions, the anomaly is weak or non‐existent. When the solar flux F10.7 index increases to 85 units the anomaly shows to be fully developed but contains a pronounced longitudinal/ seasonal dependence. During the equinoxes and afternoon hours, the northern crest extends across the South American continent, but the southern crest prevails in the eastern side of South America. It is found that the non‐linear numerical fitting of the TEC distributions can reproduce only 70% of the TEC variability.