Wind Dependency of Surface Momentum Flux in Tropical Cyclones

Tropical cyclones (TCs) are among the world’s most destructive natural disasters, imposing potentially large costs to both infrastructure and well-being. Although numerical weather prediction models have drastically advanced in tropical cyclone modeling, there is still great room for improvement. Over the past decade, TC track forecasts have improved drastically; however, TC intensity forecasts have shown little, if any, progress. In order to carry out advances in TC intensity forecasting, we must better understand the small-scale physical processes occurring within the storm. Such small processes include wind-driven momentum and enthalpy fluxes between the air-sea boundary. High winds in TCs create chaotic wave fields; thus, there is a large production of sea spray, which assists these momentum and enthalpy fluxes at the surface. These processes are extremely difficult to measure at the surface during TC conditions, so we must rely on theory and idealized models until such instrumentation is developed. Here, we focus on determining how wind speed modifies the momentum transfer under TC conditions by taking into account the effects of sea spray. We initialize Simulating WAves Nearshore (SWAN) spectral wave model implemented with a sea spray generation function and air-sea spray flux algorithm to perform two real-case tropical cyclone wave field simulations over a Gulf of Mexico domain. Different stress parameterizations taking sea spray into account are used to find a numerical model “best fit” and better determine the net momentum flux within TCs. The simulated wave spectra are compared to NDBC moored buoy data and NASA altimeter data to ensure the model produces results analogous to observations. We expect to improve the accuracy of the modeled momentum flux’s dependency on wind speeds for TC conditions to further provide improvements to TC intensity forecasts.