Abstract: In this study, we present characteristics of post-sunset GHz scintillation occurrence and their correlations with ionospheric parameters derived from ionosonde observations in high solar activity years (2012−2013) of solar cycle 24 at Sanya (18.3°N, 109.6°E; dip lat.: 12.8°N), China. The analyzed data include the F₂-layer’s critical frequency (f_oF₂), peak height (h_mF₂), and minimum virtual height (h’F), as well as the scale height around the F₂-layer peak (H_m), and virtual height (h’F₅) and true height (hF₅) measured at 5 MHz.We have investigated relationships between the equinoctial asymmetry of these scintillations and these ionospheric parameters. In addition, we calculate the growth rates of Rayleigh−Taylor instability on the basis of the ionosonde measurements and theoretical models, respectively. We find that the equinoctial asymmetry of scintillation onset time is associated with the scale length of the vertical electron density gradient (L), which has been shown to affect the growth of Rayleigh−Taylor instability at the bottom of the F-layer. The seasonal variations of f_oF₂, H_m and scale length of vertical electron density gradient appear to cause the seasonal variations of scintillation occurrence; the equinoctial asymmetry of scintillation occurrence rate over low latitudes appears to be related to background electron density and vertical drifts in the F-layer around time of sunset. Further study is required to explain the observed correlational weakness in low latitudes between scintillation strength, represented by the daily maximum S4, and daily maximum values of f_oF₂, h_mF₂, h’F, H_m, and also the drifts.