The Importance of Relative Wind Speed in Estimating Air-Sea Turbulent Heat Fluxes in Bulk Formulas: Examples in the Bohai Sea

Sea surface currents are commonly neglected when estimating the air-sea turbulent heat fluxes in bulk formulas. Using buoy observations in the Bohai Sea, this paper investigated the effects of near-coast multi-scale currents on the quantification of turbulent heat fluxes, namely, latent heat flux (LH) and sensible heat flux (SH). The maximum current reached 1 m s(-1) in magnitude, and a steady northeastward current of 0.16 m s(-1) appeared in the southern Bohai Strait. The predominant tidal signal was the semidiurnal current, followed by diurnal components. The mean absolute surface wind was from the northeast with a speed of approximately 3 m s(-1). The surface winds at a height of 11 m were dominated by the East Asian monsoon. As a result of upwind flow, the monthly mean differences in LH and SH between the estimates with and without surface currents ranged from 1 to 2 W m(-2) in July (stable boundary layer) and November (unstable boundary layer). The hourly differences were on average 10 W m(-2) and ranged from 0 to 24 W m(-2) due to changes in the relative wind speed by high-frequency rotating surface tidal currents. The diurnal variability in LH/SH was demonstrated under stable and unstable boundary conditions. Observations provided an accurate benchmark for flux comparisons. The newly updated atmospheric reanalysis products MERRA-2 and ERA5 were superior to the 1 degrees OAFlux data at this buoy location. However, future efforts in heat flux computation are still needed to, for example, consider surface currents and resolve diurnal variations.