Periodic Characteristics of Surface Electromagnetic Wave Propagation in the South China Sea

The refractive environment of the South China Sea (SCS) is currently a prominent research focus due to its significant impact on electromagnetic wave (EMW) propagation, particularly for ship-borne radar and communication systems. Based on the Global Positioning System sounding data collected during the summer monsoon period in 1998, the surface refractive conditions of the SCS were analyzed, and the relationship between these conditions and various meteorological factors was further explored. The analysis reveals a pronounced daily cycle in the surface refractive environment, closely linked to fluctuations in temperature and humidity. The modified refractivity exhibits a one-day periodicity, with the southern SCS showing a higher consistency in surface duct occurrence (96.1% probability) compared to the northern region (49.7% probability). Wind direction, particularly westerly winds, plays a significant role in enhancing surface duct strength. Numerical simulations using the Parabolic Equation method demonstrate that surface ducts significantly extend the detection range of EMW, with path loss remaining below 150 dB at 150 km under ducting conditions. These findings emphasize the operational significance of surface ducts in the SCS, particularly for over-the-horizon radar detection of low-altitude targets. Understanding the refractive environment in this region is essential for optimizing radar and communication system performance in maritime operations.