New Features of the Enhancements in Electron Density at Low Latitudes

In this study, we present some new features of the enhancements of electron density in the ionospheric F region at low latitudes. The peak parameters of the ionosphere were recorded by Sanya (109.6°E, 18.3°N) ionosonde and electron density profiles analyzed were measured by the Qujing (103.8°E, 25.6°N) incoherent scatter radar. The peak electron density of the F 2 layer ( NmF 2) is found to be enhanced in the afternoon and sunset hours. Common features in the cases demonstrate that the NmF 2 increases at low latitudes are characterized by a descent of the peak height ( hmF 2). Meanwhile, the electron density at Qujing shows an increase at the bottom of the ionosphere and a depression at topside altitudes. It is consistent with those of the ionosonde measurements at Sanya, for both the daytime and nighttime enhancements. Cross correlation analyses reveal a lag of NmF 2 to hmF 2 in the cases. After taking time shifts some events of the enhancements in NmF 2 are still associated with a downwelling hmF 2, confirming the processes which drive a lower hmF 2 and a convergence of plasma flux may possibly bring about a rise in NmF 2.