Extreme air–sea turbulent fluxes during tropical cyclone Barijat observed by a newly designed drifting buoy

Abstract

Using in situ observations collected by a drifting air–sea interface buoy (DrIB) in the northern South China Sea from August 30 to September 13, 2018, the extreme air–sea turbulent fluxes that occurred from September 8 to 13 during tropical cyclone (TC) Barijat were investigated. The most striking features were substantial increases in momentum and heat fluxes, with maximum increases of 10.8 m s⁻¹ in the wind speed (WS), 0.73 N m⁻² in the wind stress, 68.1 W m⁻² in the sensible heat fluxes (SH) and 258.8 W m⁻² in the latent heat fluxes (LH). The maximum WS, wind stress, SH and LH values amounted to 15.3 m s⁻¹, 0.8 N m⁻², 70.9 W m⁻² and 329.9 W m⁻², respectively. Using these new DrIB observations, the performance of two state-of-the-art, high-resolution reanalysis products, ERA5 and MERRA2, was assessed. The consistency of the observed values with ERA5 was slightly better than with MERRA2, reflected in higher correlations but both products underestimated the WS during TC conditions. In calm weather conditions, the turbulent heat fluxes were overestimated, because they simulated a too dry and cold atmospheric state, enhancing the air–sea differences in temperature and humidity. Considering that an accurate representation of the air–sea turbulent and momentum fluxes is essential for understanding and predicting ocean and atmospheric variability, our findings indicate that more high-quality temperature and relative humidity observations are required to evaluate and improve existing reanalysis products.