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Description:
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The nature of turbulence in the hurricane boundary layer has been the subject of much discussion . Two questions in particular continue to be the source for debate and ongoing research . The first question is whether or not hurricane GFs exhibit the same behavior as GFs from winds generated by extratropical systems (thunderstorms excluded ) . The second question is whether the structure of the wind , and the resulting gust factors , change at high wind speeds . This study seeks to address those two questions using a variety of data sources and analysis techniques . Observational data were collected from both landfalling tropical cyclones and synoptically generated extratropical wind . Analytical data at a variety of wind speeds were created using an inverse fast Fourier Transform of the universal spectrum for wind in the perturbed terrain . Gust factors and other parameters were computed for both types of data and the results assimilated in a data base .
Analysis of these data yielded interesting results . A strong dependence on surface roughness was noted for gust factors from both observed and analytical data . However , once efforts were made to control for this dependency by stratifying the data into roughness regimes using the roughness length , slight differences between the tropical and extratropical gust factor data remained . Analysis of the artificial data , suggest spectral differences between the tropical and extratropical regimes due to the presence of additional low -frequency energy in the tropical regime . A slight decrease of the gust factor with increasing wind speed was noted in the high -speed analytical data . A similar decrease was suggested in the tropical data . It was concluded that the low -frequency spectral differences between the two regimes have less of an effect on the resulting gust factors as the wind speed increases , resulting in better agreement between the two distributions . |