An experimental study of the structure of the air-flow above ocean surface waves

University Of Delaware, Newark DE

Investigators

Abstract

In recent years, considerable progress has been made in quantifying the exchange of momentum between the atmosphere and the ocean. The role of surface waves on the air-sea momentum flux is well established but our physical understanding of the airflow dynamics remains incomplete. This impedes our ability to develop improved physically based parameterizations for better weather and sea state predictions, especially in high winds and extreme conditions. In this project, the team proposes the further analysis of an existing dataset consisting of extensive high resolution 2D velocity measurements taken in the laboratory in the near surface airflow above short surface waves. It is anticipated that this work will lead to an improved understanding of the detailed, small scale physics at the air-sea interface that is necessary to build accurate coupled (ocean-atmosphere and ocean-wave-atmosphere) models of weather and climate. Furthermore, data products from this study will likely prove useful for comparison with current and future Large Eddy Simulation (LES) and Direct Numerical Simulation (DNS). This project will support the Ph.D. work of a graduate student. The importance of the surface wave in the dynamics of the coupled atmospheric and oceanic boundary layers is well recognized. In contrast, the atmospheric counterpart of this phenomenon, that is the coupling of the near surface atmospheric turbulence generated by airflow separation with the surface waves, has received less attention. To date, our incomplete understanding of the coupling between the near surface turbulence (wave or shear generated) and the surface waves remains a roadblock to the development of improved air-sea momentum flux parameterizations. Turbulence in the near surface atmospheric boundary layer is in part generated by breaking-induced airflow separation, the team thus will focus in particular on the coherence and coupling between the turbulent kinetic energy (TKE) and the surface waves. The data proposed to use covers wave ages Cp/u∗ varying from 1.4 (very young waves) to 66.7 (old waves) thus encompassing a large range of field-relevant conditions. The team proposes to extract turbulent and wave-coherent velocity fields by means of a triple velocity decomposition made possible by a wave- and phase-locked coordinate system. The team will then evaluate the turbulent kinetic balance and they will especially focus on the interaction between phase coherent turbulence and the surface waves.