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Research Seminar: Jie Gao
May 10, 2016 @ 12:20 pm - 2:20 pm
Surface wind stress is the primary force that drives the upper-ocean circulation and formation of the surface wind waves, especially under Tropical Cyclones (TCs). Current parameterization of the surface wind stress in the ADCIRC storm surge model utilizes empirical formulas of the surface drag coefficient Cd as a function of the 10 m height wind speed U10 only, in absence of considering the sea state (e.g., the Garratt’s 1977 formula, and the Powell’s storm sector-based formula). The behavior of Cd in terms of U10 varied widely from study to study, but in storm surge modeling it is generally believed that Cd increases linearly with wind speed at low to moderate winds and levels off or even decreases at high winds.
Many sea state-dependent formulas of surface stress (or equivalently the Cd or the aerodynamic roughness length z0) have been proposed based on field and laboratory studies, as the influence of waves on momentum flux at the air-sea interface has long been recognized. In this study, we propose to implement and examine five prevailing sea state-dependent formulas in the coupled ADCIRC + SWAN model to examine the behavior of Cd under high wind conditions and tailor them for shallow water application, which include the wave directional spreading-dependent Cd formula from Holthuijsen et al. (2012), the wave age-dependent z0 formula from Drennan et al. (2003), the wave steepness-dependent z0 formula from Taylor and Yelland (2001), and two wave spectrum-dependent stress formulas from Reichl et al. (2014): the RHG modified from Moon et al. (2004) and the DCCM from Donelan et al. (2012). The primary goal is to address the uncertainties in estimating surface wind stress using different methods, and propose a more physically-based, generalized method suitable for near-shore shallow water application, where mechanisms of wind-wave interaction are more profoundly complex than deep water region.