Coastal buoy observation of air-sea net heat flux in the East China Sea in summer 2020

The full fluxes and associated air-sea variables based on three months of operational buoy observations in the East China Sea (ECS) in summer 2020 were analyzed for the first time. The surface net heat flux (Q(net)) was positive (139.7 +/- 77.7 W/m(2)) and was dominated by the combined effects of solar shortwave radiation (SW) and latent heat fluxes (LH). The mean heat flux components of 4 reanalysis datasets (NCEP2, MERRA-2, CFSR, and ERA5) and buoy data were compared to assess the mean ability of the modeling/reanalysis simulation. Among the four components of air-sea flux, SW was the best simulated, while LH was the worst simulated. The longwave radiation (LW) and LH values from reanalysis were higher than those from buoy data, especially LH. The high LH resulted in low Q(net). Furthermore, the 4 reanalysis datasets were compared with the buoy dataset. Among all flux products, the difference in radiation flux was the smallest, while that in the turbulent flux was the greatest. The observed variables related to turbulent flux were analyzed to help determine the cause of the flux discrepancies. High wind speeds were the main cause of this difference. Using the variables provided by the reanalysis data and the same bulk formulas of the Coupled Ocean-Atmospheric Response Experiment (COARE 3.0), we found that the recalculated sensible heat flux (SH) and LH were closer to the observed heat fluxes than the direct model outputs. The significant differences between these methods could account for the discrepancies among different data. Among all air-sea flux products, the air-sea flux in ERA5 was closer to the in-situ observations than the other products. The comparison results of reanalysis data provide an important reference for more accurate studies of the summer heat flux in the ECS at the synoptic and climatic scales.

Automated summary

This study analyzed the full fluxes and associated air-sea variables in the East China Sea during summer 2020 using operational buoy observations. The results showed that solar shortwave radiation and latent heat fluxes were the main factors affecting surface net heat flux. The comparison of four reanalysis datasets with buoy data revealed that shortwave radiation was well simulated, while latent heat flux was poorly simulated. High wind speeds were identified as the main cause of differences in turbulent flux. The study also found that re-calculating sensible heat flux and latent heat flux using reanalysis data and the Coupled Ocean-Atmospheric Response Experiment (COARE 3.0) bulk formulas provided results closer to observed heat fluxes than direct model outputs.