The observation of Sporadic E using FT8 in JAPAN.

Sporadic E can have dramatic effects on communication in the HF and VHF bands. When sporadic E occurs, it enables communication over very long distances on these bands. Many studies, including those using ionosondes and GNSS-TEC observations, have been conducted to observe sporadic E all over the world. In this study, sporadic E propagation was investigated using FT8, one of the amateur radio digital modes, at 50 MHz in Japan. A large number of reception reports were directly collected during sporadic E events. For each received signal, the transmitting amateur radio station was identified, and its geographical location was determined from a call sign database. The midpoint between the transmitter and receiver was then used as an approximation of the reflection location of the sporadic E layer. By combining a large number of such propagation paths, the spatial distribution and movement of sporadic E were analyzed. Most of the observed structures exhibited an overall shape extending in the east–west direction, or slightly in the north–south direction, and no structures purely elongated along the north–south axis of the Japanese archipelago were observed. This tendency is consistent with observations obtained from GNSS and related measurement techniques. This study also discusses the advantages, limitations, and points for improvement of the method. The results show the effectiveness of using amateur radio stations to observe ionospheric phenomena.