VTEC behaviour in the American sector during high solar activity Original Research Article

The behaviour of the vertical total electron content (VTEC) obtained from GPS signals, received during the high solar activity year 1999 at 10 stations of the American sector, is reported. The considered latitude range extends from 18.4 to –64.7 and the longitude ranges from 281.3 to 297.7. Median, lower and upper quartiles are used to specify variability, because they have the advantage of being less affected by large deviations that can occur during magnetic storms. The results show that the VTEC values corresponding to equinox are greater than those of solstice and that the highest VTEC values are observed at low latitude stations. Moreover, these results suggest that the southern peak of the equatorial anomaly (EA) moved equator ward during this period. In general, the variability during daylight hours is about 30% of median or less, and that observed for night time hours is greater than the mentioned percentage, particularly at last hours of the night near the northern peak of the EA. The analysis shows that in some cases the quartiles are not equidistant from the median value.