F-region irregularities that cause scintillations and spread-Fechoes at low latitude

The temporal variations of two types of spread-F echoes and scintillation of stationary satellites observed at a low-latitude site are studied. The correlations among the three phenomena and with the Kp index are also investigated. Each type of spread F has quite simple variational characteristics, unlike the admixture of both types. The range spread is maximum at 2100–0100 hours during equinoxes and at high sunspot numbers, whereas the frequency spread is maximum at 0300–0500 hours during summer and at low sunspot numbers. The correlation with Kp is statistically significant for range spread, but not for frequency spread. The association of scintillation occurrence with range spread is excellent, whereas that with frequency spread is scarcely significant. The existing models of F-region irregularities that may cause the spread-F echoes and scintillations at low latitude are also discussed in the light of our findings.