Climatology and modeling of ionospheric scintillations and irregularity zonal drifts at the equatorial anomaly crest region

In this study the climatology of ionospheric scintillations and the zonal drift velocities of scintillation-producing irregularities are depicted for a station located under the southern crest of the equatorial ionization anomaly. Then, the alpha - mu ionospheric fading model is used for the first- and second-order statistical characterization of amplitude scintillations. In the statistical analyzes, data are used from single-frequency GPS receivers acquired during similar to 17 years (September 1997-November 2014) at Cachoeira Paulista (22.4 degrees S; 45.0 degrees W), Brazil. The results reveal that the nocturnal occurrence of scintillations follows the seasonal distribution of plasma bubble irregularities observed in the longitudinal sector of eastern South America. In addition to the solar cycle dependence, the results suggest that the occurrence climatology of scintillations is also modulated by the secular variation in the dip latitude of Cachoeira Paulista, since the maximum occurrence of scintillations during the peak of solar cycle 24 was similar to 20% lower than that observed during the maximum of solar cycle 23. The dynamics of the irregularities throughout a solar cycle, as investigated from the estimates of the mean zonal drift velocities, presented a good correlation with the EUV and F10.7 cm solar fluxes. Mean-while, the seasonal behavior showed that the magnitude of the zonal drift velocities is larger during the December solstice months than during the equinoxes. In terms of modeling, the results for the alpha - mu distribution fit quite well with the experimental data and with the temporal characteristics of fading events independently of the solar activity level.