Cause of surface flux variations in the South China Sea and their relation to the monsoon

The NCAR Integrated Sounding System (ISS) was installed on two research vessels (Kexue and Shiyan) during the South China Sea Monsoon Experiment (SCSMEX). The surface systems were modified to include sea snakes for measuring surface skin temperature (SST). The data have been reprocessed with stringent quality control criteria and a correction for faulty ventilation of the temperature sensors. The ventilation correction was developed using wind tunnel data and a theoretical model of the sensor/shield system. Comparisons between ship-based and buoy and satellite surface skin temperatures revealed only small biases in the ISS SSTs. The reprocessed temperature data are used to calculate bulk turbulent sensible and latent heat fluxes for the 4 IOPs. A strong cooling of the surface skin temperatures of 2 C is observed in the northern South China Sea at the Shiyan with weaker cooling at the southern base Kexue. This cooling coincides with the onset of the monsoon. The cooling has been related to both local and advective processes. Locally, the cooling is caused by increased wind speeds, decreased solar radiation and sensible cooling by precipitation. At the same time, satellite data indicate that a plume of cold water advected southward from an upwelling region along the southeast coast of China. This strong surface cooling impacts the surface fluxes in the northern S. China Sea with the distribution of surface fluxes at the two sites differing dramatically. These differences may play an important role in the evolution of the South China Sea monsoon.