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 F2 layer (NmF2) is found to be enhanced in the afternoon and sunset hours. Common features in the cases demonstrate that the NmF2 increases at low latitudes are characterized by a descent of the peak height (hmF2). 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 NmF2 to hmF2 in the cases. After taking time shifts some events of the enhancements in NmF2 are still associated with a downwelling hmF2, confirming the processes which drive a lower hmF2 and a convergence of plasma flux may possibly bring about a rise in NmF2. Key Points: Peak electron density of the F2 layer presents an increase characterized by a descent of the peak height at low latitudesNe at Qujing decreases (increases) at the topside (bottomside) of the ionosphere during the enhancement in NmF2 with a downwelling hmF2The lags between changes in hmF2 and NmF2 are applied to identify the descending hmF2 associating with increase of NmF2 [ABSTRACT FROM AUTHOR]