Heat-island-effect of ship-based bulk measurements for evaporation duct estimation

Because the evaporation duct profile is difficult to measure, different empirical surface layer models have been developed to compute the average refractivity profile near the ocean surface using four bulk measurements: pressure, temperature, humidity, wind speed at a single height (e.g., the ship’s bridge), and sea surface temperature (SST). Although these parameters can be conveniently measured using standard equipment, the measurement accuracy is usually influenced by inherent factors, such as the movement of the ship or the heat island effect. To analyze the heat island effect of ship-based bulk measurements for evaporation duct estimation, an open cruise observation over the Tropical Eastern Indian Ocean from 23 Aug 2024 to 14 Oct 2024 is used. The ship weather station measurements and the corresponding evaporation duct profiles, computed by the NPS evaporation duct model, are compared with 48 low-altitude rocketsonde profiles, which sample a high vertical resolution of air temperature, air humidity, air pressure, and wind parameters. The sensors for air temperature, humidity, pressure, and wind vector are deployed at 13.4 m above the mean sea level, and the SST is measured by an infrared thermometer. The results show that the mean air temperature and relative humidity of the ship measurements are 1.03 K and 4.07% higher than the rocketsonde measurements at the same altitude (i.e., 13.4 m), and the evaporation duct height and strength computed from the ship-based measurements are 1.98 m and 10.07 M-units lower than those from the rocketsonde measurements.