The Observed Effects of a Cold Wave on Over-the-Horizon Propagation in Evaporation Ducts Across Multiple Sea Areas

An evaporation duct is a persistent phenomenon that is formed by evaporation over the sea surface and influences marine communication and radar detection through its trapping effects. A cold wave is cold air that rapidly intensifies and intrudes a region with strong winds, a dry air mass, and precipitation, which affects the air–sea interactions and eventually affects the propagation of electromagnetic (EM) waves over the sea. However, there are few studies of over-the-horizon (OTH) propagation in evaporation duct during a cold wave. In this article, the path loss (PL) and atmospheric factors of two OTH propagation links over the Bohai Strait and Yellow Sea were observed during a cold wave in November 2021. The cold wave caused PL to decrease over 35.9 and 44.2 dB, respectively, at links over the Bohai Strait and Yellow Sea, as the evaporation duct height (EDH) simulated from the measured data increased 5.9 and 7.6 m. According to the sensitivity analysis, high wind speed (WS) was the main factor promoting seawater evaporation during the cold wave, while a decrease in air temperature (AT) had the opposite effect. These effects of cold wave should be taken into consideration in marine communication and radar detection systems to enable the optimal use.