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

This paper presents an analysis of the variability of ionospheric characteristics ( ƒ_oF2, 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 ƒ_oF2 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 ƒ_oF2 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 ƒ_oF2. Moreover, low variability was observed for M(3000)F2 and it does not vary with modip.