EGU24-2227, updated on 08 Mar 2024
EGU General Assembly 2024
© Author(s) 2024. This work is distributed under
the Creative Commons Attribution 4.0 License.

Observations of near-inertial internal wave amplification and enhanced mixing after surface reflection

Kun Liu1, Xu Chen2, Peng Zhan3, and Hui Wang1,4,5
Kun Liu et al.
  • 1Institute of Marine Science and Technology, Shandong University, Qingdao, China (
  • 2Key Laboratory of Physical Oceanography, Ocean University of China, Qingdao, China (
  • 3Department of Ocean Science and Engineering, Southern University of Science and Technology, Shenzhen, China (
  • 4Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai, China (
  • 5National Marine Environmental Forecasting Center, Beijing, China (

The overreflection process of near-inertial internal waves (NIWs) has been theoretically predicted for several decades; however, to the best of our knowledge, this phenomenon has never been comprehensively investigated in real ocean scenarios. Based on the buoy observations collected several days after the passage of Typhoon Lekima in the Yellow Sea, a NIW surface overreflection event is clearly captured. The observed NIWs undergo nearly total reflection meridionally but are amplified zonally after reflection by approximately 20% in amplitude and 56% in vertically integrated horizontal kinetic energy. Ray tracing analysis indicates that the NIW was generated in the wake of Typhoon Lekima in the area north of the Shandong Peninsula and may propagated to the buoy station as coastal-trapped internal Kelvin waves. A simulation using a slab mixed layer model suggests that local wind work was insufficient to generate the amplified NIWs. The temporal evolution of near-inertial energy also implies that the intensified near-inertial waves cannot be attributed to the spontaneous generation resulting from unbalanced flows or the parametric subharmonic instability of M2 internal tides during the reflection period. We found a high temporal correlation between the zonal NIW enhancement and the duration of a meridional lens-type shear flow after reflection, which is consistent with the Stern’s overreflection theory (Stern, 1977) that perpendicular background shear flow can feed energy to the incident NIWs. This indicates that the enhanced NIW may be stimulated by the near-surface reflection and the rotation effect plays a crucial role in the NIWs overreflection process in the real ocean. Furthermore, enhanced instability are found between the ocean surface and the upper thermocline after reflection. This study provides observational evidence that the background field could inject energy into the near-inertial band through NIW overreflection process, and may shed some light on understanding upper ocean mixing caused by NIW reflection.

How to cite: Liu, K., Chen, X., Zhan, P., and Wang, H.: Observations of near-inertial internal wave amplification and enhanced mixing after surface reflection, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2227,, 2024.