Observations of Anomalous Over-the-Horizon Propagation in the Evaporation Duct Induced by Typhoon Kompasu (202118)

Evaporation ducts, which form as a result of evaporation from the ocean, have a significant impact on electromagnetic (EM) propagation in coastal and marine environments. Theoretically, typhoons would substantially increase the mass, momentum, and heat exchanges at the air-sea interface and thus inevitably influence these EM propagation environments, including the duct conditions and propagation boundary conditions. However, the effects of typhoons on EM propagation have seldom been reported. In this study, anomalous propagation in the evaporation duct induced by Typhoon Kompasu (202118) was recorded by using an EM propagation system and automatic weather station. The length of the propagation link was 53 km, which was beyond the horizon. The evaporation duct's impact on EM propagation during Typhoon Kompasu was studied based on model simulation results. Propagation far beyond the horizon indicated that ducting was present during the typhoon passage. Furthermore, the approaching of the typhoon caused a decrease in path loss of about 20 dB. This was because the abnormal marine meteorological conditions induced by typhoons result in a high evaporation duct, which leads to a small path loss for EM propagation.