Presenter: Meng Lyu (Texas A&M University)

Description:
Near the air-sea interface, the ocean surface and lower atmosphere are strongly coupled through the exchange of momentum, mass, and heat. The transfer of momentum, which is often parameterized with the non-dimensional drag coefficient, is integral to many processes that occur at the air-sea interface. For example, momentum flux is one of the factors responsible for wave growth and breaking, surface currents, and ocean mixing. Therefore, reliable prediction of the drag coefficient is essential for accurate environmental predictions. We previously found that gustiness, which we define as rapid fluctuations in wind speed or direction, increases the drag coefficient compared to the non-gusty conditions. In this presentation, we explore the mechanisms that lead to the increase in the drag coefficient using momentum flux derived from high-frequency turbulence perturbation measurements and wave spectral data collected at sea. We will discuss the vertical and temporal variability of the drag coefficient induced by gustiness, and, in turn, their effects on waves.  These results have strong implications for weather and climate modeling and particularly for forecasting gale wind events such as hurricanes.