Researcher Qiao Fangli from the First Institute of Oceanography, Ministry of Natural Resources, along with other colleagues, utilized the tower-based observation platform in the Bohai Sea area to conduct synchronized observations of sea waves and the momentum flux of the air-sea interface. Their analysis discovered that wind wave-induced stress can correct the negative deviation between the traditional wind-generated turbulent stress and actual observations. This achievement was reported in the July 2023 “Science China Earth Sciences” issue.

The research findings of Associate Researcher Chen Sheng and Researcher Qiao Fangli et al from the First Institute of Oceanography, Ministry of Natural Resources were published in both the Chinese and English versions of "Science China Earth Sciences." The study, utilizing an offshore tower-based observation platform, designed a synchronized observation experiment for sea waves and the momentum flux of the air-sea interface. It revealed the influence mechanism of wind waves on wind stress, discovering that wind waves lead to an increase in wind stress.

The influence of waves on the wind stress at the air-sea interface has attracted more and more attention. According to different generation mechanisms, ocean waves can be divided into wind waves and swell, and there are significant differences in the regulating effects of the two on wind stress. The research team, utilizing observational data from a tower-based platform near the South China Sea coast, unveiled the impact of swell on wind stress. They found that swell reduces wind stress, and the stress induced by swell waves can correct the positive deviation between traditional wind-generated turbulence stress and observations. The related findings were published in "Geophysical Research Letters" in October 2020.

However, due to the lack of synchronized observations of wind waves and momentum flux under high wind speeds, the modulation mechanism of pure wind waves on wind stress is still unclear. Therefore, with the support of the offshore oil production plant of the Sinopec Shengli Oilfield Branch, the team designed a scientific experiment based on the tower-based platform in the southern Bohai Sea region and established a high-frequency turbulence observation system （Figure 1）， obtaining synchronized observations of wind waves and sea-air momentum flux under the influence of cold air.

Figure 1: Schematic diagram of the Bohai Tower-based Platform and Observation System.

The analysis revealed that under the influence of cold air, different wind-wave conditions caused by northwest and northeast winds result in varying wind stresses. The traditional wind-induced turbulent stress deviates from the observed momentum flux values, with the degree of deviation dependent on wind speed and wind-wave conditions. The larger the wind and waves, the greater the deviation. Wind-wave-induced stress can correct the negative deviation between traditional wind-induced turbulent stress and observed values (Figure 2). Ocean and climate numerical models need to consider the different effects of swell and wind waves on wind stress. This can be represented through wave-induced stress using a wave boundary layer model, reflecting the effects of different wave conditions.

Figure 2: Comparison of wind-induced turbulent stress (a) and the stress after wind-wave-induced stress correction (b) with observed results.

Original article: https://mp.weixin.qq.com/s/cCSJlzmursAhWo5Opl_usg