Reverse Fountain and the Nighttime Enhancement in the Ionospheric Electron Density Over the Equatorial Region: A Case Study

Abstract

AbstractThis paper focuses on the linkage between reverse fountain effect and anomalous enhancement in the nighttime electron density over the equatorial ionosphere often referred as the ionospheric nighttime enhancement (INE). The Global Positioning System (GPS)‐derived total electron content (TEC) measurements over two Indian equatorial stations and ionosonde measurements are used to investigate the occurrence characteristics and mechanism of the premidnight and postmidnight INE events. The high‐resolution spatiotemporal two‐dimensional (2D) TEC maps generated by using satellite‐based augmentation system are used to visualize the reverse fountain effect. These TEC maps are found to be effective in envisaging the motion of equatorial ionization anomaly (EIA) in nighttime ionosphere and its impact on the distribution of electron density over the equatorial region. Salient features of this case study illustrate that, accompanying enhancements in the nighttime TEC, there exist decrease in the F2 layer height, prevalence of downward vertical plasma drift, and dramatic increase in the F2 region electron density. The 2D‐TEC maps reveal the persistence of well‐developed EIA until late evening hours and its gradual shift toward equator during the events of postmidnight INEs. It is found out that the premidnight INE is not invariably linked to the prereversal enhancement of the zonal electric field and could be associated with the redistribution of electron density caused by the reverse fountain effect. The present observations indicate that although the westward electric field serves as a prime driver, the INEs over the equatorial regions are associated with plasma motions caused by the retreating anomaly.