The near-inertial internal wave is a significant energy source for deep-sea mixing. However, the energy source of deep near-inertial internal waves remains largely unknown.
Recently, the research team led by Prof. WANG Fan from the Institute of Oceanology of the Chinese Academy of Sciences (IOCAS) has made new progress in the study of the generation mechanism of deep near-inertial kinetic energy.
The study was published in Geophysical Research Letters on Dec. 23.
Researchers used observation data from a full-depth mooring located at 130°E/15°N over three years and found that tropical cyclones can trigger near-inertial internal waves that can penetrate into 3000 m layer. Such waves contribute more than 50% to the deep near-inertial kinetic energy.
Meanwhile, internal tides can also generate the deep near-inertial kinetic energy through parametric sub-harmonic instability, but such a mechanism can only contribute less than 30% to the deep near-inertial kinetic energy.
Researchers found that during the observation period, four tropical cyclone events passed through the observation area and triggered different vertical propagation characteristics of near-inertial internal waves. "It was discovered that under the modulation of stronger intermediate and deep warm eddies, wind-generated near-inertial internal waves experience faster downward propagation speeds and lower energy loss rates during the downward propagation process," said ZHANG Zhixiang, firtst author of the study.
Besides, the presence of intermediate and deep warm eddies contributes to improving the energy conversion efficiency of the parametric sub-harmonic instability mechanism, allowing for the energy transfer from diurnal internal tides to near-inertial internal waves even north of the critical latitude.
"This study emphasizes that accurately simulating intermediate and deep eddy activity and the intensity of tropical cyclone wind stress is crucial for improving the simulation accuracy of intermediate and deep near-inertial kinetic energy," said Prof. WANG.
The time-depth variation of the near-inertial kinetic energy observed by the mooring
Zhang, Z., Gao, J., Wang, J., & Wang, F. (2024). Contributions of tropical cyclones and internal tides to deep near-inertial kinetic energy under eddy modulation. Geophysical Research Letters, 51, e2024GL111330.
(Text by ZHANG Zhixiang)
Media Contact:
ZHANG Yiyi
Institute of Oceanology
E-mail: zhangyiyi@qdio.ac.cn
(Editor: ZHANG Yiyi)