The Air-Sea Interface as a Factor in Rapid Intensification of Tropical Cyclones
American Geophysical Union Fall Meeting, Washington, DC, December 10-14, 2018
Data assimilation, Remote sensing, Tropical cyclones, Extreme events
Observations suggest that under extreme wind speed conditions there is a widespread disruption of the air-sea interface. The mechanisms that control disruption of the air-sea interface in tropical cyclones are somewhat analogous to the process of atomization that is well studied in such engineering applications as fuel injection in combustion and cryogenic rocket engines, food processing, and inkjet printing. The related instabilities may include the well-known interfacial mode (Kelvin-Helmholtz instability) and the “liquid” mode (which has some resemblance to the Holmboe instability). In this work, computational fluid dynamics experiments have been performed using a multi-phase volume of fluid large eddy simulation model (ANSYS Fluent) to reproduce properties of the air-sea interface under tropical cyclone conditions. A very fine resolution mesh 0.75 mm x 0.75 mm x 0.75 mm and a realistic surface tension coefficient (0.072 N/m) were set at the air-water interface. The model was forced with hurricane force wind stress at the top of the air layer. The periodic boundary condition along the wind direction was equivalent to an infinite fetch. The model reveals a noticeable asymmetry between the air and water sides of the interface (most of the action is on the air side), which has previously been observed in laboratory experiments. Such asymmetry is typical for the Kelvin-Helmholtz instability at a gas-liquid interface with a significant density difference. Computational and laboratory experiments have resulted in the development of a non-monotonous parameterization of the air-sea drag coefficient dependence on wind speed that can contain the aerodynamic drag well near 60 m/s wind and can explain the rapid intensification and rapid decline of tropical cyclones (Soloviev et al., JGR-Oceans, 2017). One serious complication is that the enthalpy exchange coefficient is still a poorly known parameter in tropical cyclones. A volume of fluid to discrete phase model is under development for a more realistic enthalpy exchange parameterization. We are considering other related factors involved in the tropical cyclone intensification and decline including vapor advection in the cyclone, coupled air-sea system effects, and atmospheric conditions.
Soloviev, Alexander; McGauley, Michael G.; and Dean, Cayla W., "The Air-Sea Interface as a Factor in Rapid Intensification of Tropical Cyclones" (2018). Marine & Environmental Sciences Faculty Proceedings, Presentations, Speeches, Lectures. 542.