Comparison of GPS-TEC measurements with IRI2012-TEC predictions in the Brazilian sector during the unusual solar minimum 2009

Abstract

The total electron content (TEC) derived from two Global Positioning System (GPS) receivers localized at Palmas (PAL, 10.2°S, 48.2°W, dip latitude 5.5°S), near equatorial region, and São José dos Campos (SJC, 23.2°S, 45.9°W, dip latitude 17.6°S), under the southern crest of the equatorial ionization anomaly (EIA), in the Brazilian sector are used in this paper. TEC from the latest available IRI-2012 model at the same locations is also used. A comparative study between GPS-TEC and the IRI-2012 model is analyzed during the deep low solar activity period of 2009 in the unusual solar cycle 23. The measurements and the modeled data show that the IRI-TEC model gives the better estimates of the GPS-TEC during the nighttime from January to December months at PAL and SJC. The IRI-TEC model shows larger differences from the GPS-TEC in the afternoon hours, mainly at SJC. These discrepancies observed at SJC in the afternoon hours for all months are possibly due to the dynamics of EIA in consequence of the equatorial fountain effect. At PAL and SJC, oscillations of GPS-TEC with periods around 16 days in April and periods around 27-32 days between September and December possibly are noticed which could be related to a modulation of the semidiurnal tide and Sun’s rotation, respectively. Also, oscillations with periods around 2-4 and 5-10 days from January to December are observed at PAL and SJC, possibly associated with the propagation of planetary waves.