Date of Award
Master of Science in Oceanography
The ocean temperature (especially the Sea Surface Temperature (SST) is very important to the formation and development of tropical cyclones. Warm water from the sea surface evaporates and provides energy to drive hurricanes. As a tropical cyclone passes over the ocean, the SST behind it becomes significantly cooler than what it was prior to the hurricane's arrival. The surface temperature declines as a result of turbulent mixing as well as upwelling following a divergence of surface currents. This cooling (hereafter the "cold wake") is important to understand in order to develop better tropical cyclone models. The key to modeling this is the momentum flux budget at the air-sea interface.
Current models assume that the momentum flux into the ocean currents is equal to the wind stress. However, this does not take into account momentum lost to or gained from a growing or decaying surface wave field or from wave-induced Coriolis-Stokes forcing. This study seeks to develop a fully coupled ocean-wave model to enhance understanding of the air-sea momentum flux budget in tropical cyclones and as a result improve models of the cold wake. The ocean model component used is the Princeton Ocean Model (POM) with a 1/12 degree resolution and 23 half sigma levels. It calculates the ocean temperature and currents driven by a prescribed wind stress interpolated from hurricane message files generated by the National Hurricane Center. The wave model used is Wave Watch 3.14 and also has a 1/12 degree resolution. It uses a prescribed wind speed based on the same hurricane message file and calculates the momentum flux lost to or gained from a growing or decaying wave field and the momentum flux lost to or gained from Coriolis-Stokes forcing. In the coupled model, the ocean currents are used in the wind stress calculations and in the wave model component.
Results of idealized and real hurricane simulations demonstrate clearly that the altered wind stress (by including the ocean current effect), wave momentum flux budget, and Coriolis-Stokes forcing significantly alter the momentum flux into the ocean currents and in turn the cold wake. While the wave momentum flux budget and reduced wind stress decrease the surface cooling, the Coriolis-Stokes forcing may lead to increased surface cooling. It is also shown that these three effects can alter the latent heat flux that fuels hurricanes.
Hughes, Colin J., "AIR-SEA MOMENTUM FLUX IN A COUPLED OCEAN-WAVE MODEL AND ITS IMPACT ON THE OCEAN RESPONSE TO A HURRICANE" (2014). Open Access Master's Theses. Paper 289.