Langmuir Turbulence Under Tropical Cyclones

Brandon Reichl,
Tetsu Hara,
Isaac Ginis,

This is project is funded by the National Science Foundation

In collaboration with: Tobias Kukulka (University of Delaware)

The program is aimed at understanding Langmuir circulation (LC) under realistic Tropical Cyclone (TC) conditions and at assessing the role of LC on the coupled ocean-wave-atmosphere TC dynamics. We are testing our hypothesis that LC effects will have a significant effect on the three-dimensional TC dynamics and prediction by applying synergistically a coupled atmosphere-wave-ocean model and a turbulence resolving large eddy simulation model (LES) that captures LC. We, thus, examine an insufficiently understood turbulent process, LC, that is not explicitly represented in most ocean models, despite the fact that LC may be a principal mixing component. We are working on advancing the scientific basis of TC models and improve their prediction skill, which will ultimately lead to increased reliability of hurricane forecasts and thus confidence in the official hurricane warnings.

Major Activities

Significant exchange between the URI, UD, and University of Washington (UW) research groups has been taken place. UD and URI groups have held regular phone meetings to discuss our latest results and to decide the next steps for advancing the project. A conference-call meeting between URI, UD, and UW (Eric D’Asaro and Ramsey Harcourt) also took place. The URI team has supplied the UD team with time dependent wind and numerical wave data during Tropical cyclone Gustav conditions. The UW team has supplied the UD team with time dependent float data under Hurricane Gustav, including upper ocean turbulence data and temperature and salinity profiles. The UD team has forced a turbulence simulation model with these data. All three teams interpreted jointly the simulated turbulence fields and compared results to observations.

Significant Results

Upper ocean turbulence under hurricane Gustav

TKE budgets of Langmuir cells (large-scale coherent structures)

Langmuir turbulence in non-equilibrium swell conditions

Figure 1. Hurricane Gustav simulation. LC direction predicted with Lagrangian Shear direction (black line). Red = Wind direction, black = Lagrangian Shear direction, blue = Surface Stokes drift direction.

Figure 2. Hurricane Gustav simulation. Normalized VKE: w2/u*2.