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  • March 19, 2019
  • Gao, Jie
    • Affiliation: College of Arts and Sciences, Department of Marine Sciences
  • When wind blows over the open water, it exerts a shear stress at the water surface that transfers horizontal momentum vertically downward across the air–sea interface, driving the upper-ocean circulation, non-tidal sea surface elevation fluctuation, and formation of the surface wind waves. Thus, an accurate estimate of the surface wind stress is crucial to atmospheric, storm surge, and wave modeling. In this study, we have two major objectives: 1) development of a Generalized Asymmetric Holland Model (GAHM), and 2) implementation and evaluation of different surface drag laws for storm surge modeling. Two major improvements over the classic Holland Model (HM) were made in this study. First of all, the assumption of cyclostrophic balance at radius to the maximum wind (RMW) was removed to eliminate the influence of the Rossby number (Ro) on the gradient wind solution. Secondly, a composite wind method was employed to synthesize storm information from multiple storm isotachs. The GAHM has been fully implemented in the ADCIRC model for real-time storm surge forecast, and initial model evaluation indicated an improved forecasting skill over the classic HM, especially when dealing with TCs with a small Ro. It is generally accepted by the storm surge modeling community that the surface drag coefficient Cd increases linearly with wind speed at low to moderate winds and levels off or even decreases at high winds. In this study, several sea state dependent surface drag laws, including two explicit momentum flux models (RHG and DCCM), were implemented to study their behaviors under various wind and wave regimes, and to address the uncertainties in storm surge modeling. Initial evaluation suggested that the wave saturation tail level plays a big role in determining the surface stress, and the influence of the resolved part of the spectrum can be relatively small. Also, surge patterns were found to be greatly influenced by the spatial patterns of Cd, indicating a large uncertainty in storm surge modeling when using different drag laws. In the future, surge data of real hurricane cases are needed to quantify the performance of each drag law.
Date of publication
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Rights statement
  • In Copyright
  • Luettich, Rick
  • Rosman, Johanna
  • Dietrich, Casey
  • Blanton, Brian
  • Bane, John
  • Doctor of Philosophy
Degree granting institution
  • University of North Carolina at Chapel Hill Graduate School
Graduation year
  • 2018

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