Variation characteristics of sporadic-E layer in East Asia based on long-term data

Abstract

Sporadic E (Es) is a transient electron density enhancement structure that occurs at altitude of 90–140 km. With the increasing number of global ionosonde stations and the accumulation of long-term data, conducting research on the long-term variations of the Es layer using synchronized data from multiple stations over extended periods holds significant scientific importance. Eastern Asia is located in the peak region of the Far East Anomaly of the Es layer and possesses unique geographical advantages. In this study, we extensively investigated the characteristics of Es layer intensity, spatial distribution, diurnal variation, seasonal variation, and long-term variations in the Eastern Asian region using observation data spanning over 60 years from 21 ionosonde stations in China and Japan. It is found that the Es layer intensity in East Asia is much higher than the global average level, and the intensity center is located near the 30° N line, and weakens to low and high latitudes. At the same time, the intensity center of Es layer is not fixed, and the intensity center migrates with diurnal and seasonal variations. In East Asia, the long-term variation trend of Es layer intensity at different locations is different, but overall, it presents a long-term upward trend and has a negative feedback characteristic. The obtained research findings hold crucial scientific significance for exploring the formation mechanisms of the Es layer, analyzing the spatiotemporal distribution and long-term trends of Es layer intensity.