A Case Study of the Enhancements in Ionospheric Electron Density and Its Longitudinal Gradient at Chinese Low Latitudes

The day-to-day variability of the ionospheric electron density and its longitudinal gradient challenges our description and understanding of the ionosphere, which is also essential for reliable applications of the Global Navigation Satellite System (GNSS). In this paper we conduct a case study of the anomalous enhancements in ionospheric electron density and its longitudinal gradient to reveal the spatial extent and related drivers of the enhancements. The ionospheric data analyzed include the vertical total electron content (TEC) by the Global Navigation Satellite System receivers, peak electron density (NmF2) and height (hmF2) of the F layer by a chain of ionosondes, and electron density profiles recorded by the Qujing incoherent scatter radar (103.8 degrees E, 25.6 degrees N) during the period from 29 May to 2 June 2015. Electron density enhancements are found in the region around the northern crest of equatorial ionization anomaly on the first 2 days of June 2015. It is the first time to report that, during the anomalous enhancement, the increase in electron density over Qujing depends on altitude, being stronger at higher altitudes. Further, there are strong longitudinal gradients in vertical TEC in the regions during the course of the electron density enhancements. Low latitude hmF2 and especially the equatorial electrojet become much larger on the enhancement days, implying the important role of equatorial zonal electric fields in the formation of the electron density enhancements at low latitudes. Key Points Electron density enhances strongly in the ionospheric F region at Chinese low latitude close to the equatorial anomaly crest Increase in electron density depends on altitude, being stronger at higher altitudes A strong longitudinal gradient and zonal electric field is accompanying with the enhancement in electron density