Continuous observation of evaporation ducts in Super Typhoon Koinu (202314) using clustered wave gliders: mechanisms and maritime communication implications

Formed by humidity stratification in the marine atmospheric boundary layer, evaporation ducts serve as critical natural channels for maritime over-the-horizon (OTH) wireless communication. Their unique structure effectively confines electromagnetic (EM) wave propagation, substantially enhancing the link stability and transmission quality of long-range maritime communication while exerting notable impact on OTH EM wave propagation. Tropical cyclones profoundly alter near-surface meteorological conditions and disrupt the distribution uniformity of evaporation ducts, directly inducing fluctuations in communication link path loss (PL), intensified signal attenuation, and even short-term outages, severely impairing maritime broadband communication. However, direct and mobile observations of evaporation ducts within typhoon interiors remain limited. This study investigated the evolution of evaporation duct height (EDH) during Typhoon Koinu (202314) through analysis of 108 hours of continuous observations by three clustered wave gliders. One glider traversed the typhoon eye, while the other two monitored regions of high wind speed (WS). The maximum recorded WS reached 26.5 m/s, accompanied by EDH of 11.9 m, whereas within the eye region, WS was 4.36 m/s with EDH of 5.7 m. The presence of the typhoon’s eye caused a 6.2-m reduction in EDH. Relative humidity (RH) fluctuated from 70% to 95% before the typhoon’s arrival and remained at around 90% during the typhoon’s passage. Correlation analysis indicated that RH was the dominant factor influencing EDH before the typhoon’s arrival, showing negative correlation (Spearman correlation coefficient: −0.83). In contrast, WS was the main driver of EDH variation during the typhoon’s passage, exhibiting strong positive correlation (Spearman correlation coefficient: 0.82). Sensitivity analysis confirmed that the inhibitory effect of elevated RH outweighed the contribution of high WS to EDH enhancement, leading to lower EDH values during the passage of the typhoon than in the pre-typhoon period. Analysis of the spatial distribution of EM wave propagation indicated that the low EDH induced by low WS in the typhoon’s eye caused PL that was 24 dB greater than under high-WS scenarios; overall, the presence of the typhoon’s eye caused greater PL.