Behavior of Evaporation Ducts in Stable and Unstable Surface Layers

Abstract The atmospheric surface layer over the ocean has a strong impact on electromagnetic (EM) wave propagation in the lowest 100 m of the atmosphere. Due to surface evaporation, a strong vertical gradient in water vapor forms in this layer, resulting in an evaporation duct which may greatly increase detection ranges for sensors and targets within the duct. When a warm air mass moves over cooler water, the surface layer forms a stable thermal stratification whose ducting characteristics are much less understood compared to its counterpart, the unstable surface layer. In this study, we perform a sensitivity study to examine the characteristics of the stable surface layer profiles and how their impacts on EM propagation differ from those in the unstable cases. Using buoy‐based measurements from both coasts of the United States as input to a surface layer model, refractivity profiles were generated as input to a propagation model to characterize path loss. The results suggest that the stable surface layers present more complex propagation scenarios with a broad range of propagation loss including the maximum propagation loss in the subrefractive conditions and maximum trapping in cases of deep evaporation duct heights. The results also suggest strong dependance of propagation loss on evaporation duct height when the transmitter height is above the duct. In contrast, propagation loss is no longer sensitive to evaporation duct height once the transmitter is within the duct. This research also reveals the role of 2‐m curvature of the M‐profile in defining the propagation regimes.