Statistical characteristic and correlation of low latitude F region bottom-type irregularity layers and plasma plumes over Sanya 

Lianhuan Hu - Institute of Geology and Geophysics, Chinese Academy of Sciences 

Session: Thermosphere-Ionosphere Interactions and Effects

Abstract

VHF radar observations of ionospheric F region bottom-type irregularity and plasma plumes over the low latitude station Sanya (18.4°N, 109.6°E) during the equinoctial months of 2011-2018 are analyzed. The results show an equinoctial asymmetry in the occurrence of F region backscatter plumes, wherein the occurrence could be greater in spring or autumn months under different solar activity and background ionospheric conditions. On the other hand, the bottom-type irregularity layer occurred almost exclusively in the descending phase of solar cycle (2015-2018). No clear correlation is found between the occurrences of bottom-type irregularity layer and plasma plume at low latitude. The F layer virtual height  observations from the Sanya ionosonde show that the average h’F is higher during the months when the plume occurrence is higher, suggesting that the asymmetric plasma vertical drift could play a role in the equinoctial asymmetry of plume occurrence. Larger vertical drift (and higher h’F) could cause higher occurrence of equatorial plasma plumes which extend to low latitudes along magnetic field lines. In contrast, the h’F is relatively lower during the days when bottom-type irregularity layers occur. We surmise the background h'F could play a negative role in the generation of bottom-type irregularity layer at low latitude.