GPS-VTEC measurements and IRI predictions in the South American sector Original Research Article

Vertical total electron content (VTEC) measurements obtained with GPS satellite signals during 1999 are used to check the validityof the international reference ionosphere (IRI) to predict this ionospheric variable in the South American sector. Measurements obtained during June solstice and September equinox at nine stations are used. The considered latitude range extends from 18.4 to −64.7 and the longitude ranges from 281.3 to 297.7. The deviation between modelled and measured values was obtained. The results show that, in general, for both seasons IRI over-estimatesVTEC at night-time and sunrise hours. Better predictions were obtained in the latitude range (18.4°, −33.1°) for the period 8–22 LT. For high latitude stations, IRI does not give good predictions. Additional studies covering more stations and conditions and using ionosonde data will be useful to complete the IRI validation.