Morphological Characteristics Of Thousand-Kilometer-Scale E-S Structures Over China

Sporadic E (E-s) structures have been observed occasionally covering a large horizontal scale of more than 1,000 km over China. Their onset locations and propagation features, and related generation mechanisms still remain unknown. In this study, a statistical analysis of large-scale E-s structures is performed based on the ionospheric total electron content obtained from ground-based receiver networks, in combination with data from multiple ionosondes in China. The large-scale strong E-s structures mainly occur during summer months, with dominant horizontal azimuth in the east-west and northwest-southeast directions and dimensions of 1,000-3,000 km along the elongation. They predominantly drift southwestward at the speed of 30-210 m/s. The main onset region for the large-scale E-s structures over China is identified for the first time, which is around 20 degrees-45 degrees N and 100 degrees-125 degrees E. Based on the morphological features of large-scale E-s structures, and the observation of concurrent cases of traveling ionospheric disturbances, we surmise that gravity waves could play an important role in the generation of large-scale E-s structures.