Response of sea surface heat fluxes to the South China Sea summer monsoon onset in 2021

Abstract

By using the ship-based data collected over the South China Sea during the South China Sea summer monsoon (SCSSM) in 2021, the characteristics of near-surface meteorological conditions, surface heat budget, and atmospheric boundary layer structure are analyzed. We found that near-surface air temperature (relative humidity) decreased significantly during the developed monsoon period, while near-surface wind speed showed an obvious increase trend from the pre-monsoon period to the developed monsoon period. The significant reduction of solar radiation due to cloud cover led to the reverse of oceanic heat flux direction from downward to upward. The sea surface sensible and latent heat fluxes were restrained after the SCSSM onset. The atmospheric boundary layer height presented a positive (negative) correlation with near-surface air temperature (humidity). In addition, the vertical profiles of wind speed, virtual potential temperature, and air humidity revealed that: after monsoon onset, (i) the atmospheric circulation within the atmospheric boundary layer accelerated, with a strong low-level jet located below 500-m height; (ii) there was a strong inversion layer below 500-m height, especially at 1300 and 1900 local time (LT); (iii) the atmospheric humidity in low-level raised significantly. • Near-surface meteorological conditions before and after the South China Sea summer monsoon (SCSSM) onset in 2021 were compared. • Responses of sea surface heat budget to the SCSSM onset in 2021 were revealed. • Characteristics of atmospheric boundary layer structure during the SCSSM period were discussed.