Characteristics of the Marine Evaporation Duct Height Climatology over the Tropical Indian Ocean and the Effect of the Marine Atmospheric Boundary Layer

Abstract The marine atmospheric boundary layer influences the evolution of evaporation duct height (EDH) by altering the vertical profile of the refractive index. The EDH is a crucial parameter for marine and naval communication. Many studies have demonstrated the sensitivity of boundary layer similarity theory in estimating the vertical profile of refractive index. The current study modifies the widely accepted EDH formulation of Babin’s model A to suit the air–sea interaction in moderate wind conditions of the tropical Indian Ocean (TIO), referred to as a modified model A (MMA). The EDH estimated by the MMA model has reduced the error by around 3.5 m than that of the operational Paulus–Jeske (PJ) model, when validated against observations. The present study revealed that the PJ model fails in an upwelling region and also modifies the seasonality of computed EDH. Shapley additive explanations (SHAP) analysis brings out that the EDH is sensitive to moisture transfer coefficient (with R 2 = −0.83) and surface layer stability (with R 2 = 0.8) in the TIO, which was supported by the hourly time series constructed from ocean buoy data. This study brings confidence in replacing the existing operational PJ model with the MMA model in naval applications for the TIO region. Significance Statement To compute evaporation duct height (EDH), Babin’s model A is a well-accepted model to overcome the problems with the previous Paulus–Jeske (PJ) model. To suit the wind conditions over the tropical Indian Ocean, the model A has been slightly modified (modified model A). Comparison analysis showed that the PJ model precisely fails in an upwelling region rather than in a stable surface layer region as found in previous studies. Comparing all the marine atmospheric boundary layer (MABL) variables, surface layer stability is found to be the most dominant variable determining the EDH. In an unstable and neutral surface layer, the sea–air humidity difference and moisture transfer coefficient affect the EDH, and in a stable surface layer, additionally, humidity and sea surface temperature affect the duct height variability.