Langmuir circulation scheme outperforms wave orbital mixing in northwestern Pacific model

Choosing the right way to represent ocean waves inside an ocean model can make the difference between a realistic simulation and a badly biased one, according to a new evaluation of two wave-induced mixing schemes in the northwestern Pacific. The study, published in Ocean Dynamics, compared a scheme based on Langmuir circulation with one based on wave orbital motion during the stratified seasons of 2018, testing each against a control run with no wave-induced mixing at all.

Non-breaking waves stir the upper ocean even when they never crest, and regional ocean models need a parameterization to capture this turbulence. The Langmuir circulation scheme represents non-local mixing driven by the interaction of surface waves with wind forcing, while the wave orbital motion scheme treats mixing locally, relying only on wave parameters to describe turbulence generated by the orbital velocities of passing waves.

Both schemes enhanced vertical mixing in the upper 100 meters of the model ocean relative to the control experiment. But their performance diverged sharply. The Langmuir circulation scheme improved the simulation of the mixed layer depth, the boundary between wind-stirred surface water and the stratified water beneath, and generally showed better agreement with satellite and in-situ observations than the control run.

The wave orbital motion scheme told a different story. It overestimated vertical mixing, producing an overly deep mixed layer and a pronounced cold bias in sea surface temperature, particularly in the northern part of the model domain, where the simulation chilled the surface even though observations did not show such cooling.

The researchers traced the source of the problem to a fundamental limitation of wave-based parameterizations. Their analysis showed that the wave orbital velocity and the turbulent Langmuir number, a scale that compares wind-driven and wave-driven turbulence, were nearly uncorrelated, because the Langmuir number incorporates both wave and wind effects. That means wave parameters alone cannot characterize non-breaking wave-induced mixing, which provides a physical explanation for why the orbital motion scheme overestimates turbulence.

The lesson is that mixing under stratified conditions depends on the combined effects of surface waves and local wind forcing, not on wave state by itself. The Langmuir circulation formulation, by including both wave and wind information, adapts to varying conditions and delivers a more realistic representation of upper-ocean mixing, including in cases where the mixed layer is shallow.

The practical implication for modelers is direct: purely wave-driven formulations risk stirring the simulated upper ocean too vigorously, biasing mixed layer depth and sea surface temperature, while schemes grounded in the joint wave-wind dynamics of Langmuir circulation better capture the observed structure of the upper ocean in this region.

The study compared two representative schemes over the stratified seasons of a single year in one regional domain, so the results describe this model configuration and period rather than a universal verdict on wave mixing physics. Even so, the evaluation offers clear guidance for regional ocean modeling in the northwestern Pacific.

Subject of Research: Evaluation of non-breaking wave-induced mixing parameterization schemes in a northwestern Pacific regional ocean model

Article Title: Evaluation of wave-induced mixing schemes in a northwestern pacific ocean model

Article References: Liu, T., Hirose, N., Yoshikawa, Y., & Lee, E. (2026). Evaluation of wave-induced mixing schemes in a northwestern pacific ocean model. Ocean Dynamics, 76(11), Article 115. https://doi.org/10.1007/s10236-026-01872-x

Image Credits: AI Generated

DOI: 10.1007/s10236-026-01872-x

Keywords: ocean modeling, wave-induced mixing, Langmuir circulation, mixed layer depth, sea surface temperature, northwestern Pacific, turbulent Langmuir number, upper ocean turbulence, parameterization, Ocean Dynamics, Evaluation, wave-induced