Occurrence Tendency Analysis of Sporadic E-Layer in Korea

Sporadic E (Es) Layer refers a thin layer of enhanced electron density in the ionospheric E region, where the electron density can be 2 to 3 times higher than the surrounding areas, reaching up to 1012 m–3. The Es layer typically has a thickness of about 1–2 km and extends horizontally over i tens to hundreds of kilometers. It is a significant factor influencing radio wave propagation in the high-frequency (HF) and very-high frequency (VHF) bands. The daily and monthly occurrence frequencies were analyzed, and correlation analysis was performed with solar activity and geomagnetic disturbances. The critical frequency of Es (foEs) values were highest near noon in the summer, while h'Es peaked at 06:00, decreased until noon, and then increased again around 16:00. Seasonally, the highest virtual height of Es (h’Es) values where observed in April, followed by a decrease until August, after which they began to rise again. At Icheon station, the occurrence of Es layer was more frequent at 12:00 and 20:00, with the highest seasonal frequency observed in June. In contrast, the Jeju station showed a peak occurrence around 11:00, and also recorded the highest seasonal frequency in June. The incidence of Es layer was generally higher during solar minimum compared to solar maximum. This results will be used to develop a machine learning model for predicting for occurrence of Es layer.