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Abstract

This study presents observational findings of air-sea turbulent heat flux anomalies during the onset of the South China Sea summer monsoon (SCSSM) in 2021 and explains the mechanism for high-resolution heat flux variations. Turbulent heat flux anomalies are not uniform throughout the basin but indicate a significant regional disparity in the South China Sea (SCS), which also experiences evident year-to-year variability. Using buoy- and cruise-based air-sea measurements, high-temporal (hourly) anomalies in the latent heat flux during the SCSSM burst are unexpectedly determined by sea-air humidity differences under near-neutral marine atmospheric boundary layer (MABL) stability conditions, with secondary wind effects. However, latent heat anomalies are mainly induced by wind speed under mixed unstable and near-neutral MABL conditions. The sensible heat flux is much weaker, with its anomalies dominated by sea-air temperature differences regardless of the boundary layer condition. The observational results are used to examine the discrepancies in turbulent heat fluxes and associated air-sea variables in reanalysis products. The comparisons indicate that latent and sensible heat fluxes in the reanalysis are overestimated by approximately 52 Wm^-2 and 3 Wm^-2, respectively. These overestimations are mainly induced by higher sea-air humidity/temperature estimates. The relative humidity is underestimated by approximately 6.4% in two high-resolution reanalysis products. The higher SST (near-surface specific humidity) and lower air temperature (specific air humidity) eventually lead to higher estimates of sea-air humidity/temperature (2.2 g·kg^-1/0.6 °C), which are the dominant factors controlling the variations in the air-sea turbulent heat fluxes.