Date of Award
2025
Degree Type
Dissertation
Degree Name
Doctor of Philosophy in Oceanography
Specialization
Physical Oceanography
Department
Oceanography
First Advisor
Isaac Ginis
Second Advisor
Tetsu Hara
Abstract
This Ph.D. dissertation presents a numerical modeling study of wave-current interactions in tropical cyclones. Chapter 1 focuses on wave-current interaction in shallow water during hurricane landfall, when strong winds often generate severe storm surges that dramatically raise water levels and cause significant damage to human lives and property. Large waves generated by these winds further amplify storm surges, making it necessary to couple storm surge models with wave prediction models. Currently, two-dimensional coupled storm surge-wave models incorporate the effect of waves on the storm surge through the forcing of radiation stress gradients. However, recent studies on wave-current interactions indicate that this approach does not capture the complete impact of waves on storm surge and ocean currents. In this study, the governing equations solved by a two-dimensional storm surge model are rewritten in terms of the vertically integrated Lagrangian (Eulerian+Stokes drift) current, instead of the vertically integrated Eulerian current, to account for a more detailed effect of waves on currents and water elevation. The wave forcing in the updated momentum equation includes the radiation stress gradients and one additional term which depends on both waves and currents. The impact of this new wave forcing term on the storm surge was examined, by including it in the Advanced Circulation storm surge model, coupled with the Wavewatch III wave model, and performing storm surge simulations under Hurricane Michael (2018) and Ian (2022). In both cases, radiation stress leads to a significant increase of water levels (~0.4 m) over an extended region on the right side of the storm. On the other hand, the new wave forcing mainly leads to a reduction in water levels, which is quite substantial (~0.3 m) close to the storm track and is associated with strong currents and waves propagating in the same direction shortly before landfall.
Chapter 2 focuses on wave-current interactions in tropical cyclones in deep waters. Surface waves generated by tropical cyclones not only have an impact on the upper ocean, but in turn are affected by ocean currents themselves. Since storm-generated waves can be destructive even in deep-water conditions, affecting oil platforms and ship navigation, it is essential to couple ocean models with surface wave models, to accurately predict wave fields under tropical cyclones. In this study, the impact of currents on surface deep-water waves generated by idealized tropical cyclones of varying size, intensity and translation speed, is investigated using the Modular Ocean Model 6, coupled with the Wavewatch III wave model. The mixing scheme parameterization used by the ocean model includes the effect of sea-state dependent Langmuir turbulence, while the wave model is forced by the sum of the surface Eulerian current computed by the ocean model and a wave modulation term that originates from the enhancement of the apparent group speed of dominant waves due to nonlinear interactions with coexisting waves. In all cases examined, the inclusion of ocean currents in wave simulations results in a notable reduction of the maximum significant wave height (0.5-2.1 m, ~9%), as dominant waves propagate faster due to advection by currents and remain under strong wind forcing for shorter periods of time. Additionally, substantial differences between wave simulations using different current definitions emphasize the importance of accurately representing the reduction of surface currents due to wave-induced Langmuir turbulence and including the enhancement of the dominant wave group velocity by coexisting waves.
Chapter 3 investigates the impact of wave-current interactions in real hurricanes in the Gulf of Mexico. We use the coupled Modular Ocean Model 6 - Wavewatch III model and the standalone Wavewatch III model to simulate Hurricane Ian (2022), Hurricane Idalia (2023) and Hurricanes Helene and Milton (2024). Including currents in the wave simulations produces reductions in the significant wave height and peak period in the region of the largest storm-generated waves. These reductions are pronounced in deep waters. Although they weaken with decreasing depth, they remain substantial over the 20-70 m depth range. The model results are evaluated by comparing them with observations from drifting buoys during the four storms. In cases where the impact of currents on significant wave height and peak period is small, the mean bias between observations and model predictions is relatively small, indicating that the model has sufficiently good skill in predicting the two wave parameters. In cases where the impact of the currents is substantial, including them reduces the mean bias by more than a factor of two, revealing a notable improvement in model accuracy.
Recommended Citation
Papandreou, Angelos, "COUPLED NUMERICAL MODELING OF WAVE-CURRENT INTERACTIONS IN TROPICAL CYCLONES" (2025). Open Access Dissertations. Paper 4518.
https://digitalcommons.uri.edu/oa_diss/4518