Limited Sea Surface Temperature Cooling Due to the Barrier Layer Promoting Super Typhoon Mangkhut (2018)

This study investigates the impact of the salinity barrier layer (BL) on the upper ocean response to Super Typhoon Mangkhut (2018) in the western North Pacific. After the passage of Mangkhut, a noticeable increase (∼0.6 psu) in sea surface salinity and a weak decrease (< 1°C) in sea surface temperature (SST) were observed on the right side of the typhoon track. Mangkhut-induced SST change can be divided into the three stages, corresponding to the variations in BL thickness and SST before, during, and after the passage of Mangkhut. During the pre-typhoon stage, SST slightly warmed due to the entrainment of BL warm water, which suppressed the cooling induced by surface heat fluxes and horizontal advection. During the forced stage, SST cooling was controlled by entrainment, and the preexisting BL reduced the total cooling by 0.89°C d⁻¹, thus significantly weakening the overall SST cooling induced by Mangkhut. During the relaxation stage, the SST cooling was primarily caused by the entrainment. Our results indicate that a preexisting BL can limit typhoon-induced SST cooling by suppressing the entrainment of cold thermocline water, which contributed to Mangkhut becoming the strongest typhoon in 2018.