Statistics of spread F characteristics across different sectors and IRI 2016 prediction

Abstract

The occurrence of the plasma irregularity and the related scintillation have been extensively investigated as a result of the impact on radio signal propagation. This study focused on the equatorial spread F (ESF) occurrence using ionogram data and IRI prediction taken across different longitude sectors, including the Jicamarca, Fortaleza, Ilorin, Chumphon and Kwajalein ionosonde stations. We have briefly discussed the varying range type spread F (RSF) occurrence features across these stations such as the duration, onset time and seasonal asymmetry. The largest seasonal average of the RSF occurrence percentage was recorded at the Ilorin station during the low solar activity, while the occurrence rate at the Chumphon and Kwajalein stations increases significantly with the solar flux intensity. Furthermore, we presented a comparative analysis of the observed RSF occurrence rate and the IRI model prediction. The result exhibited a significant error percentage across these longitudes. The IRI could not reproduce significant features such as the delayed RSF onset at the Kwajalein station during June solstice or the equinox asymmetry in the RSF occurrence across these longitudes. Surprisingly, the IRI model also performed poorly at the Brazilian longitude. These observations highlight the strong dynamic nature of the RSF features across the different regions. Hence, an extensive dataset of the RSF occurrence distribution selected with cognizance for the longitudinal pattern of the major factors controlling the phenomenon is considered necessary for the further improvement of the empirical model.