Microphysics of the air-sea interface under tropical cyclone conditions: Computational fluid dynamics simulation and laboratory experiment
Alexander V. Soloviev (1, 2), Michael G. McGauley (1), Mark A. Donelan (2), Brian K. Haus (2), Nathan Laxague (2), David Ortiz-Suslow (2), Isaac Ginis (3), Roger Lukas (4)
(1) Oceanographic Center, Nova Southeastern University, Dania Beach, Florida
(2) Rosenstiel School of Marine and Atmospheric Science, University of Miami, Florida
(3) Graduate School of Oceanography, University of Rhode Island, Narragansett, Rhode Island
(4) Department of Oceanography, University of Hawaii at Manoa, Honolulu, Hawaii
Missing and unresolved physics at the air-sea interface are among the factors limiting tropical cyclone predictions. In a laboratory experiment at Air-Sea Interaction Salt Water Tank (ASIST) and coordinated numerical simulation with the Volume of Fluid Large Eddy Simulation (VOF LES), conducted in this work, the microstructure of the air-water interface under hurricane force wind resembled Kelvin-Helmholtz shear instability between fluids with large density difference.
Supported by these data, we bring forth the concept that the resulting two-phase environment suppresses short gravity-capillary waves and alters the aerodynamic properties of the sea surface. The unified wave-form and two-phase parameterization model developed in our work shows the well-known increase of the drag coefficient with wind speed, up to ~30 m/s. Around 60 m/s, new parameterization predicts a local minimum of the drag coefficient. This feature may explain rapid intensification of some storms to major tropical cyclones and the observed bi-modal distribution of tropical cyclone maximum intensity. Implementation of the new parameterization of the drag coefficient in operational models (GFDL, HWRF) is expected to improve predictions of tropical cyclone intensity, storm surge, and the associated wave field.