Day-to-day variability of ionospheric characteristics in the American sector Original Research Article

This paper presents an analysis of the variability of ionospheric characteristics (ƒoF2, M(3000)F2) measured at Americanlatitudes (latitudinal range: −65.2, 18.5). The database includes ionograms recorded during different seasonal and solar activity conditions. The parameters used are: median, lower and upper quartiles. Two parameters are considered: Cup = upper quartile/ median, and Clo = lower quartile/median. The diurnal, seasonal and latitudinal behaviour of the variability is analysed for low and high solar activity. The variability parameters for four typical time periods of the day (22-02LT; 05-07LT; 10-14LT; 18-20LT) are presented for different seasons and the two levels of solar activity. The results indicate that the variability of ƒoF2 is high in low solar activity and larger at night than during the day. Most of the considered cases have shown that the variability of ƒoF2 has a latitudinal dependence. For some cases the variability was maximum at modip ≅ ±30. The fact that the quartiles are not equidistant from the median value suggests that it would be convenient to develop a model on Cup and Clo in order to predict the variability range of ƒoF2. Moreover, low variability was observed for M(3000)F2 and it does not vary with modip.