Air‐sea interface in hurricane conditions

Abstract

[1] Improving hurricane prediction models requires better understanding of complex processes taking place at the air-sea interface at high wind speeds. The change of the air-sea interaction regime in hurricane conditions has been linked to the mechanism of direct disruption of the air-sea interface by pressure fluctuations working against the surface tension force. This can be achieved through the Kelvin-Helmholtz type instability. In order to investigate this mechanism, we have conducted a series of 3D numerical experiments using a volume of fluid multiphase model. The experiments were initialized with either a flat interface or short wavelets and wind stress applied at the upper boundary of the air layer. The direct disruption of the air-water interface and formation of two-phase transition layer were observed in the numerical model under hurricane force wind. The vertical profiles of density and velocity in the transition layer were consistent with the regime of marginal stability, which permitted estimation of the lower limit on the drag coefficient under hurricane conditions. This limit was appreciably lower than the wave resistance law; though, it was gradually increasing with wind speed. The numerical experiments with imposed short wavelets demonstrated the tearing of wave crests, formation of water sheets and spume ejected into the air, smoothing of the water surface, as well as quasiperiodic structures on the top of wave crests resembling the Tollmien-Schlichting instability. This study can help in developing a framework for combining the effects of the two-phase environment with the contribution to the drag from waves.

The air-sea interface and surface stress under tropical cyclones

“…Laboratory22 and numerical27 experiments, conducted with monochromatic waves, unexpectedly demonstrated that KH instability of the air-water interface does take place, though predominantly near wave crests. The local conditions near the wave crest are more favorable for KH instability development because the instantaneous interfacial shear near wave crests is higher than the time-averaged shear.…”

“…The VOF 3D LES model27 included realistic sea surface tension and was forced with wind stress corresponding to U 10 ≈ 40 ms -1 . The images are taken with a shadow-imager in a small air-sea interaction tank at ASIST at wind speed corresponding to U 10 ≈ 40 ms −1 as well.…”

Is the State of the Air‐Sea Interface a Factor in Rapid Intensification and Rapid Decline of Tropical Cyclones?

“…Figure shows the results of a numerical experiment performed with the multiphase volume of fluid large eddy simulation (VOF LES) computational fluid dynamics model described in Soloviev et al (). A very fine mesh with the spatial resolution at the air‐water interface mm 3 was used in this work (versus mm 3 in Soloviev et al, ). The surface tension coefficient at the air‐water interface was set at 0.072 N m −1 ; periodic boundary conditions were set along the x axis; and slippery boundary conditions at the bottom and side walls.…”

Surface waves and wave‐coupled effects in lower atmosphere and upper ocean

“…The environmental extremes have been gaining significant attention over recent years, and this topic is well reflected in the current special issue. Papers by Soloviev et al [2012], Liu et al [2012], Holthuijsen et al [2012]are dedicated to air‐sea interface and boundary layer in the hurricane‐like conditions. Specifically, Liu et al [2012]suggested a new parameterization for wind stress which takes into account the spray effects in the boundary layer and is able to describe the sea drag across all weather conditions, from low‐ to hurricane‐like winds and agrees with the available observations Holthuijsen et al [2012]…”