Sea-state Dependence of Sea Surface Temperature Cooling and its Feedback on Tropical Cyclone Intensity

Air-sea momentum and heat fluxes underneath tropical cyclones (TCs) are important controls on storm intensity. Increased upper ocean mixing due to TC winds can upwell cooler waters to the surface, reducing the heat flux from the ocean and weakening the storm. Therefore, improved representation of the wind forcing and the resulting sea surface temperature cooling in coupled ocean-wave-atmosphere models can help increase the accuracy of intensity predictions. However, the impact of surface waves (sea state) on these processes is not fully understood. The three most significant sea state dependent effects on upper ocean processes are the Coriolis-Stokes forcing, the air-sea flux budget (effect of growing/decaying surface waves), and the Langmuir turbulence (enhancement of the upper ocean mixing due to surface waves). In this study we focus on the first two effects.

To examine these two effects a comparison is made using a series of idealized storms, with a range of translation speeds, with individual and combined implementations of these two components in a fully coupled ocean-wave-atmosphere model. The Princeton Ocean Model is used with a 1/12^th degree resolution and 23 half-sigma levels and an initial temperature profile based on the Gulf of Mexico climatology. It is coupled to the WaveWatch III wave model, also at 1/12^th degree resolution. The atmospheric component is the NOAA/GFDL hurricane model, which has 42 vertical levels and a three-level nested mesh. The inner two meshes are 1/18^th and 1/6^th degree resolution, with the finer inside the coarser, and move with the storm.

It is found that both the Coriolis-stokes forcing and the sea state dependent air-sea flux modify the magnitude and the spatial distribution of the sea surface cooling, and that the combined effect may significantly modify the storm intensity predictions.