Air-Sea Momentum Transfer in Extreme Wind Conditions

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Hurricanes develop and intensify by "feeding" off the energy of warm oceanic waters. This air-sea interaction is a key factor in numerical modeling of hurricanes, but how this interaction changes in very high wind speeds is unknown due to the difficulty of making measurements in major hurricanes. This project will make use of a large wave tank at the University of Miami that can generate winds of Category 5 hurricane intensity to fill the current gap in observations and to study the roles of wind and waves in air-sea interactions. The project has the potential to improve numerical modeling of hurricanes, which directly impacts public safety and the economy. The research team also plans to engage the public through a variety of outreach mechanisms, such as social media and facility tours. The project will also help to train the next generation of scientists.The research team plans to establish new relationships for the air-sea momentum exchange in extreme wind and wave conditions with a focus on improving hurricane modeling. The main goal of the project is to identify the roles of various wind and wave related processes in controlling the air-sea momentum transfer in high winds, and to measure the rate of transfer in such conditions. The possible mechanisms cited by the research team are: sheltering of the air flow in the lee of steep breaking waves, enhanced dissipation of waves by wind, and vertical density gradient decrease due to spray and foam entrainment. The researchers hypothesize that the air-sea momentum transfer undergoes a fundamental change of governing physical processes between low-to-moderate, high, and extreme wind conditions. To address this hypothesis, four main tasks are laid out: 1) Conduct a series of laboratory experiments in the SUrge-STructure-Atmosphere INteraction (SUSTAIN) facility at the Univ. of Miami; 2) Derive a new relationship between air-sea momentum flux and mean wind, wave-state, and spray concentration and streak coverage; 3) Formulate a new wind input source function; and 4) Conduct numerical simulations in a fully coupled atmosphere-wave-ocean model and validate against field observations.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.