Edge Plasma Enhancements of Equatorial Plasma Depletions Observed by All-Sky Imager and the C/NOFS Satellite

Equatorial plasma depletions (EPDs) appearing at nighttime low latitudes were widely studied before. The edge plasma enhancements of equatorial plasma depletions (EPEEPDs) were repeatedly observed by the all-sky imager and the Communications/Navigation Outage Forecasting System (C/NOFS) satellite. However, the two-dimensional structures of EPEEPDs have not been well addressed. In this study, the airglow observations from one all-sky imager showed that the EPEEPDs occurred only in the east and west edges of EPDs but not at the poleward edge as earlier reported from the in situ measurements of low Earth orbit satellites. Four-year observations (2012-2015) from both our all-sky imager and the C/NOFS satellite have been analyzed. Compared to the airglow images, the in situ observation from C/NOFS showed that the edge plasma enhancements appeared to be less prominent with respect to the background, but both showed that the plasma enhancement was a high-incidence phenomenon, and the average incidence reached about 82% during days with EPDs observed. The occurrence of EPEEPDs showed similar characteristic as EPDs, such as the longitudinal dependences. The zonal extension of EPEEPDs showed different scale characteristics at different altitudes; its zonal extent varied with its altitudinal dependence. Four-year observations from C/NOFS satellite showed that the occurrence of EPEEPDs peaked during 20:00-22:00 LT. The result from all-sky imager showed that the relative intensity enhancement appeared contemporaneously, with maximal relative intensity exceeding 90%. We suggest that the generation mechanism of EPEEPDs is possibly related to the polarized electric field of EPDs. The plasma is more likely to be redistributed and exhibits as depletion and enhancement.