Turbulence in the Wave Boundary Layer

Turbulence in the Wave Boundary Layer

air‑sea interaction, turbulence, ocean waves.

General context of the study

Ocean waves directly impact the turbulence in the lower part of the atmosphere. This region impacted is called the wave boundary layer (WBL). The international height for wind and turbulence measurements is 10 meters. The WBL often reaches over 100 meters in height, therefore these measurements are often within the WBL itself and therefore strongly influenced by the ocean’s waves (Chalikov and Belevich, 1993). If the impact of the ocean waves is not considered when handling analysis of captured wind data, the results can be skewed to misrepresent the true behavior of the atmosphere in applications such as weather forecasting and site assessment for offshore wind energy. The latter aspect can be visualized by recognizing that offshore wind turbines typically have a hub height around 150 meters, causing their blades to sweep in and out of the WBL.

The goal of this project is to work synergistically with France Energies Marines and install additional instruments on their platform DRACCAR to capture fully the effect of the ocean surface waves on the turbulence in the wave boundary layer. Specifically, the spectrum of the ocean surface waves is imprinted on the WBL turbulence spectrum, in both aspects of time and space. Simultaneously, regional simulations of the Fécamp Wind Farm will be run that attempt to capture the WBL numerically. The experimental data will then be compared to the modelling outputs and said comparison will be used to improve the current models of the air‑sea interface and the lower atmosphere.

Detailed research program

• Determine the applicability of Monin‑Obukhov Similarity Theory at the Fécamp site (similar to work of Ortiz‑Suslow et al., 2021).
• Perform a case study around synoptic conditions, such as the passage of cyclones, and its effect on the WBL turbulence (similar to Huang et al., 2021).
• Take turbulence data from mast measurements to more accurately inject turbulence into the DOROTHY model, for numerical experimentation.
• Investigate and develop more accurate local scale parameterisations (<1 km) from mast data and integrate into WRF.
• Compare and contrast with prior parameterisations and make connections between local and regional scales.
• Compare higher resolution WRF runs with new parameterisations to satellite datasets, to compare spatial representation.
• Use integrated parameterisations in WRF to run local scale wind farm simulations.

Different steps of the work

1. Bibliography on wave boundary layer and air‑sea coupling in regional models.
2. Assist in the experimental set‑up and maintenance of instruments (FEM/DRACCAR).
3. Compile and run regional atmospheric, oceanic, and wave models in an HPC environment (CRIANN).
4. Programmatic analysis of the observation and modelled data.
5. Writing scientific publications and participation to an international conference.

References

• (Chalikov and Belevich, 1993) Chalikov, D. V. and Belevich, M. Y. (1993). One‑dimensional theory of the wave boundary layer. Boundary‑Layer Meteorology, 63(1–2) :65–96.
• (Huang et al., 2021) Huang, J., Zou, Z., Zeng, Q., Li, P., Song, J., Wu, L., Zhang, J. A., Li, S., and Chan, P.-w. (2021). The turbulent structure of the marine atmospheric boundary layer during and before a cold front. Journal of the Atmospheric Sciences, 78(3) :863–875.
• (Ortiz‑Suslow et al., 2021) Ortiz‑Suslow, D. G., Kalogiros, J., Yamaguchi, R., and Wang, Q. (2021). An evaluation of the constant flux layer in the atmospheric flow above the wavy air‑sea interface. Journal of Geophysical Research: Atmospheres, 126(8).

The desired candidate has a strong understanding of the atmospheric surface layer, air‑sea interaction, and turbulent exchange. They will have both experimental and numerical interests and feel comfortable using and compiling scientific code in an HPC environment.